staging: rtl8188eu: os_dep: Remove return variable

Remove return variable as its value is not altered between
initialisation and return.
Issue found with Coccinelle.

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