staging: rtl8188eu: cleanup comparsion to NULL in usb_halinit.c

Use if(!x) instead of if(x == NULL).
Reported by checkpatch.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Link: https://lore.kernel.org/r/20190726180448.2290-6-straube.linux@gmail.com


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