staging: rtl8712: 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/20200919085032.32453-1-straube.linux@gmail.com


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