Fixes fate-qtrle-32bit on big-endian.

The macro does a simple byte swap on uint8 array without any casts, so
it's valid on big-endian arches.

The mentioned test was failing because the byteswap function
shuffle_bytes_3210_c() is used in the pixel format conversion
(argb->bgra).
Reviewed-by: NMichael Niedermayer <michael@niedermayer.cc>
Signed-off-by: NAndriy Gelman <andriy.gelman@gmail.com>