swscale: Fix aarch64 and i386 compilation failures This unbreaks builds after c1a0e657638f7007dcc807a2d985c22631fcd6d3, which broke with errors like src/libswscale/aarch64/rgb2rgb.c:66:25: error: incompatible function pointer types assigning to 'void (*)(const uint8_t *, uint8_t *, uint8_t *, uint8_t *, int, int, int, int, int, const int32_t *)' (aka 'void (*)(const unsigned char *, unsigned char *, unsigned char *, unsigned char *, int, int, int, int, int, const int *)') from 'void (const uint8_t *, uint8_t *, uint8_t *, uint8_t *, int, int, int, int, int, int32_t (...)