iio:pressure:mpl3115: Fix sparse cast to restricted __be32 warning

>> >> drivers/iio/pressure/mpl3115.c:101:46: sparse: cast to restricted __be32
>> >> drivers/iio/pressure/mpl3115.c:115:46: sparse: cast to restricted __be32

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>