arm: dsputil: Drop restrict keyword from add_pixels_clamped_armv6 prototype

The function is assigned to a function pointer that does not have the
restrict keyword for that parameter.

This fixes compilation for MSVC builds that don't recognize "restrict",
broken since ed9625eb62.

libavcodec/arm/dsputil_init_armv6.c

@@ -29,8 +29,7 @@ void ff_simple_idct_armv6(int16_t *data);
 void ff_simple_idct_put_armv6(uint8_t *dest, int line_size, int16_t *data);
 void ff_simple_idct_add_armv6(uint8_t *dest, int line_size, int16_t *data);
 
-void ff_add_pixels_clamped_armv6(const int16_t *block,
-                                 uint8_t *restrict pixels,
+void ff_add_pixels_clamped_armv6(const int16_t *block, uint8_t *pixels,
                                  int line_size);
 
 void ff_get_pixels_armv6(int16_t *block, const uint8_t *pixels, int stride);