x86/swscale: use unsigned to build SIMD values to avoid signed overflow

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/x86/swscale.c

@@ -188,7 +188,7 @@ void updateMMXDitherTables(SwsContext *c, int dstY, int lumBufIndex, int chrBufI
                 *(const void**)&lumMmxFilter[4*i+0]= lumSrcPtr[i];
                 lumMmxFilter[4*i+2]=
                 lumMmxFilter[4*i+3]=
-                ((uint16_t)vLumFilter[dstY*vLumFilterSize + i])*0x10001;
+                ((uint16_t)vLumFilter[dstY*vLumFilterSize + i])*0x10001U;
                 if (CONFIG_SWSCALE_ALPHA && alpPixBuf) {
                     *(const void**)&alpMmxFilter[4*i+0]= alpSrcPtr[i];
                     alpMmxFilter[4*i+2]=
@@ -199,7 +199,7 @@ void updateMMXDitherTables(SwsContext *c, int dstY, int lumBufIndex, int chrBufI
                 *(const void**)&chrMmxFilter[4*i+0]= chrUSrcPtr[i];
                 chrMmxFilter[4*i+2]=
                 chrMmxFilter[4*i+3]=
-                ((uint16_t)vChrFilter[chrDstY*vChrFilterSize + i])*0x10001;
+                ((uint16_t)vChrFilter[chrDstY*vChrFilterSize + i])*0x10001U;
             }
         }
     }