staging:rtl8723au: Fix sparse warning cast to restricted __le16

This patch fixes the following sparse warning:

drivers/staging/rtl8723au/hal/rtl8723a_bt-coexist.c:343:36: warning:
cast to restricted __le16

by using the le16_to_cpus function.

Signed-off-by: Tobenna P. Igwe <ptigwe@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>