staging: rtl8723bs: do not use __constant_cpu_to_le16

cpu_to_le16() is capable enough to detect __builtin_constant_p()
and to use an appropriate compile time ___constant_swahbXX()
function.

So we can use cpu_to_le16() instead of __constant_cpu_to_le16().

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>