avutil/common: Fix undefined shift

av_mod_uintp2_c uses a bitwise AND with (1 << p) - 1 to clear the high
bits of an unsigned int. But this is undefined if p == 31, because 1 is
an int and 2^31 is not representable in an int. So make 1 unsigned.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/common.h

@@ -240,7 +240,7 @@ static av_always_inline av_const unsigned av_clip_uintp2_c(int a, int p)
  */
 static av_always_inline av_const unsigned av_mod_uintp2_c(unsigned a, unsigned p)
 {
-    return a & ((1 << p) - 1);
+    return a & ((1U << p) - 1);
 }
 
 /**