Make some type conversions explicit

Change-Id: I35e1126e567a949267898bb0fc95c518db98999a

aom_dsp/fastssim.c

diff --git a/aom_dsp/fastssim.c b/aom_dsp/fastssim.c
index 74f7515..1b93c31 100644
--- a/aom_dsp/fastssim.c
+++ b/aom_dsp/fastssim.c
@@ -345,11 +345,11 @@
         unsigned g2;
         unsigned gx;
         unsigned gy;
-        g1 = abs(im1[(j + 1) * w + i + 1] - im1[j * w + i]);
-        g2 = abs(im1[(j + 1) * w + i] - im1[j * w + i + 1]);
+        g1 = abs((int)im1[(j + 1) * w + i + 1] - (int)im1[j * w + i]);
+        g2 = abs((int)im1[(j + 1) * w + i] - (int)im1[j * w + i + 1]);
         gx = 4 * FS_MAXI(g1, g2) + FS_MINI(g1, g2);
-        g1 = abs(im2[(j + 1) * w + i + 1] - im2[j * w + i]);
-        g2 = abs(im2[(j + 1) * w + i] - im2[j * w + i + 1]);
+        g1 = abs((int)im2[(j + 1) * w + i + 1] - (int)im2[j * w + i]);
+        g2 = abs((int)im2[(j + 1) * w + i] - (int)im2[j * w + i + 1]);
         gy = 4 * FS_MAXI(g1, g2) + FS_MINI(g1, g2);
         gx_buf[(j & 7) * stride + i + 4] = gx;
         gy_buf[(j & 7) * stride + i + 4] = gy;