staging: rtl8192u: Fix type mismatch warnings reported by sparse

Mk16_le() is an inline function returning le16_to_cpu()
which is causing type mismatch warnings. Removed Mk16_le() and
replaced it with le16_to_cpu() with appropriate argument type as
suggested by Greg K-H.

Signed-off-by: Suniel Mahesh <suniel.spartan@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>