staging: r8723au: Fix sparse warning in os_dep/os_intfs.c

Sparse reports the following:

drivers/staging/rtl8723au/os_dep/os_intfs.c:321:14: warning: restricted __be16 degrades to integer

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>