vpx_ports/mem_ops.h: clear some -Wconversion warnings

not strictly necessary, but allows projects using '-Wconversion
-Wno-sign-conversion' to reuse these headers.

Change-Id: Id1398d726c90173ccba9aea66798fcef6f20fa23
diff --git a/vpx_ports/mem_ops.h b/vpx_ports/mem_ops.h
index d4a3d77..1f8f914 100644
--- a/vpx_ports/mem_ops.h
+++ b/vpx_ports/mem_ops.h
@@ -168,8 +168,8 @@
 static VPX_INLINE void mem_put_be16(void *vmem, MEM_VALUE_T val) {
   MAU_T *mem = (MAU_T *)vmem;
 
-  mem[0] = (val >> 8) & 0xff;
-  mem[1] = (val >> 0) & 0xff;
+  mem[0] = (MAU_T)((val >> 8) & 0xff);
+  mem[1] = (MAU_T)((val >> 0) & 0xff);
 }
 
 #undef  mem_put_be24
@@ -177,9 +177,9 @@
 static VPX_INLINE void mem_put_be24(void *vmem, MEM_VALUE_T val) {
   MAU_T *mem = (MAU_T *)vmem;
 
-  mem[0] = (val >> 16) & 0xff;
-  mem[1] = (val >>  8) & 0xff;
-  mem[2] = (val >>  0) & 0xff;
+  mem[0] = (MAU_T)((val >> 16) & 0xff);
+  mem[1] = (MAU_T)((val >>  8) & 0xff);
+  mem[2] = (MAU_T)((val >>  0) & 0xff);
 }
 
 #undef  mem_put_be32
@@ -187,10 +187,10 @@
 static VPX_INLINE void mem_put_be32(void *vmem, MEM_VALUE_T val) {
   MAU_T *mem = (MAU_T *)vmem;
 
-  mem[0] = (val >> 24) & 0xff;
-  mem[1] = (val >> 16) & 0xff;
-  mem[2] = (val >>  8) & 0xff;
-  mem[3] = (val >>  0) & 0xff;
+  mem[0] = (MAU_T)((val >> 24) & 0xff);
+  mem[1] = (MAU_T)((val >> 16) & 0xff);
+  mem[2] = (MAU_T)((val >>  8) & 0xff);
+  mem[3] = (MAU_T)((val >>  0) & 0xff);
 }
 
 #undef  mem_put_le16
@@ -198,8 +198,8 @@
 static VPX_INLINE void mem_put_le16(void *vmem, MEM_VALUE_T val) {
   MAU_T *mem = (MAU_T *)vmem;
 
-  mem[0] = (val >>  0) & 0xff;
-  mem[1] = (val >>  8) & 0xff;
+  mem[0] = (MAU_T)((val >> 0) & 0xff);
+  mem[1] = (MAU_T)((val >> 8) & 0xff);
 }
 
 #undef  mem_put_le24
@@ -207,9 +207,9 @@
 static VPX_INLINE void mem_put_le24(void *vmem, MEM_VALUE_T val) {
   MAU_T *mem = (MAU_T *)vmem;
 
-  mem[0] = (val >>  0) & 0xff;
-  mem[1] = (val >>  8) & 0xff;
-  mem[2] = (val >> 16) & 0xff;
+  mem[0] = (MAU_T)((val >>  0) & 0xff);
+  mem[1] = (MAU_T)((val >>  8) & 0xff);
+  mem[2] = (MAU_T)((val >> 16) & 0xff);
 }
 
 #undef  mem_put_le32
@@ -217,10 +217,10 @@
 static VPX_INLINE void mem_put_le32(void *vmem, MEM_VALUE_T val) {
   MAU_T *mem = (MAU_T *)vmem;
 
-  mem[0] = (val >>  0) & 0xff;
-  mem[1] = (val >>  8) & 0xff;
-  mem[2] = (val >> 16) & 0xff;
-  mem[3] = (val >> 24) & 0xff;
+  mem[0] = (MAU_T)((val >>  0) & 0xff);
+  mem[1] = (MAU_T)((val >>  8) & 0xff);
+  mem[2] = (MAU_T)((val >> 16) & 0xff);
+  mem[3] = (MAU_T)((val >> 24) & 0xff);
 }
 
 #endif  // VPX_PORTS_MEM_OPS_H_