staging/rtl8188eu : Remove duplicated BIT() definitions

The BIT() macro is already defined in bitops.h, remove duplicate
definitions. Users of BIT() macro are expecting unsigned int/u32, so
add typecasts where this creates a build warning.

Signed-off-by: Anish Bhatt <anish@chelsio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>