mesa/formats: don't byteswap when building array formats

mesa/formats: don't byteswap when building array formats

Because we build here an array format, we don't need to swap the
bytes for big endian.
If it isn't an array format, the bytes will be swapped in
_mesa_format_convert.

v2: remove temp variable

Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>