Staging: kpc2000: kpc_dma: Remove comparison to NULL.

Comparison to NULL been used across the driver,
remove them and use (!var) instead.

Checkpatch.pl: CHECK:
Comparison to NULL could be written "!desc"... etc

Signed-off-by: Sam Muhammed <jane.pnx9@gmail.com>
Link: https://lore.kernel.org/r/f344afba0a8bb0413941a63678688435f04a96b4.1585143581.git.jane.pnx9@gmail.com


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