Fixes checkpatch warning "Comparison to NULL could be written [...]".

Signed-off-by: Simon Sandström <simon@nikanor.nu>
Link: https://lore.kernel.org/r/20190704060811.10330-4-simon@nikanor.nu


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