av1/common/filter: fix int. sanitizer warnings

implicit conversion from type 'int' of value -2 (32-bit, signed) to type
'uint16_t' (aka 'unsigned short') changed the value to 65534 (16-bit,
unsigned)

BUG=aomedia:2357

Change-Id: I4180e23a64292620763f5646fd04fc2b11d618b2

av1/common/filter.h

diff --git a/av1/common/filter.h b/av1/common/filter.h
index 7ae4672..806b52d 100644
--- a/av1/common/filter.h
+++ b/av1/common/filter.h
@@ -263,7 +263,7 @@
 
 static INLINE void reset_interp_filter_allowed_mask(
     uint16_t *allow_interp_mask, DUAL_FILTER_TYPE filt_type) {
-  uint16_t tmp = ~(1 << filt_type);
+  uint16_t tmp = (~(1 << filt_type)) & 0xffff;
   *allow_interp_mask &= (tmp & ALLOW_ALL_INTERP_FILT_MASK);
 }