staging: qlge: fix comparison to NULL warning

Fix comparison to NULL by replacing with !ptr instead.
 Issue detected by checkpatch.

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Link: https://lore.kernel.org/r/20191010214006.23677-4-jbi.octave@gmail.com


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