staging: rtl8192u: ieee80211: Replace bit shifting with BIT macro

Change suggested by coccinelle.

Replace bit shifting on 1 with the BIT(x) macro.
Coccinelle script:

@@
expression c;
@@

-(1 << c)
+BIT(c)

Signed-off-by: Vatsala Narang <vatsalanarang@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>