staging: rtl8192u: clean up comparsions to NULL

Clean up comparsions to NULL reported by checkpatch.
if (x == NULL) -> if (!x)
if (x != NULL) -> if (x)

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20200919150823.16923-3-straube.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>