ARM: fix missing MUL16() return type

Originally committed as revision 17679 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/arm/mathops.h

@@ -81,7 +81,7 @@ static inline av_const int64_t MAC64(int64_t d, int a, int b)
 
 /* signed 16x16 -> 32 multiply */
 #   define MUL16 MUL16
-static inline av_const MUL16(int ra, int rb)
+static inline av_const int MUL16(int ra, int rb)
 {
     int rt;
     __asm__ ("smulbb %0, %1, %2" : "=r"(rt) : "r"(ra), "r"(rb));