staging: qlge: Avoid NULL comparison

Replace NULL comparison with boolean negation. Issue found using checkpatch.pl

Signed-off-by: Nachammai Karuppiah <nachukannan@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Link: https://lore.kernel.org/r/1572940458-109252-1-git-send-email-nachukannan@gmail.com


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