staging: rtl8192e: Fix comparisons to NULL

Checkpatch prefers the shorter version (x / !x) over
(!= NULL / == NULL), respectively.

Signed-off-by: Davidson Francis <davidsondfgl@gmail.com>
Link: https://lore.kernel.org/r/20210215194441.11430-1-davidsondfgl@gmail.com


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