staging: most: fix sparse warning Using plain integer as NULL pointer

This patch fixes following sparse warning:
Using plain integer as NULL pointer
in drivers/staging/most/dim2/dim2.c

Signed-off-by: Marcin Ciupak <marcin.s.ciupak@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>