staging: gasket Fix comparison with Null

Comparison with NULL is redundant
as pointer will evaluate to true if is non-NULL.
The change was suggested by checkpatch.pl.

Signed-off-by: Mayank Suman <mayanksuman@live.com>
Link: https://lore.kernel.org/r/PS1PR04MB2934D85E82A3730349F56FE9D6849@PS1PR04MB2934.apcprd04.prod.outlook.com


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