m68knommu: fix use of cpu_to_le() on IO access

Due to the different data endian requirements of different buses on
m68knommu variants we sometimes need to byte swap results for readX()
or values to writeX(). Currently the code uses cpu_to_le to do this,
resulting in sparse warnings like:

arch/m68k/include/asm/io_no.h:78:16: sparse: sparse: cast to restricted __le32

Some casting to force __le32 types would resolve but it looks to be
simpler to just switch to using the underlying swab32() to resolve.

Similarly handle the 16bit cases in these functions as well.

Reported-by: kernel test robot <lkp@intel.com>
CC: Marc Kleine-Budde <mkl@pengutronix.de>
Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>