lavc/ppc/h264dsp: Fix function prototype after bc26fe89.

Silences the following gcc warnings:
src/libavcodec/ppc/h264dsp.c: In function 'ff_h264dsp_init_ppc':
src/libavcodec/ppc/h264dsp.c:809:40: warning: assignment from incompatible pointer type
src/libavcodec/ppc/h264dsp.c:810:40: warning: assignment from incompatible pointer type
src/libavcodec/ppc/h264dsp.c:811:40: warning: assignment from incompatible pointer type
src/libavcodec/ppc/h264dsp.c:812:40: warning: assignment from incompatible pointer type

libavcodec/ppc/h264dsp.c

@@ -771,12 +771,12 @@ void biweight_h264_W_altivec(uint8_t *dst, uint8_t *src, int stride, int height,
 }
 
 #define H264_WEIGHT(W) \
-static void weight_h264_pixels ## W ## _altivec(uint8_t *block, int stride, int height, \
+static void weight_h264_pixels ## W ## _altivec(uint8_t *block, ptrdiff_t stride, int height, \
                                                 int log2_denom, int weight, int offset) \
 { \
     weight_h264_W_altivec(block, stride, height, log2_denom, weight, offset, W); \
 }\
-static void biweight_h264_pixels ## W ## _altivec(uint8_t *dst, uint8_t *src, int stride, int height, \
+static void biweight_h264_pixels ## W ## _altivec(uint8_t *dst, uint8_t *src, ptrdiff_t stride, int height, \
                                                   int log2_denom, int weightd, int weights, int offset) \
 { \
     biweight_h264_W_altivec(dst, src, stride, height, log2_denom, weightd, weights, offset, W); \