staging: rtl8192u: Change type of rtl8192_rx_initiate()

Change type of function rtl8192_rx_initiate from int to void as it
always returns 0 and this value is never used.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>