staging: wfx: le16_to_cpus() takes a reference as parameter

staging: wfx: le16_to_cpus() takes a reference as parameter

Original code caused an (100% reproducible) invalid memory access on
big-endian targets.

Fixes: b0998f0c040d "staging: wfx: add IRQ handling"
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191008094232.10014-4-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>