firmware: stratix10-rsu: fix warnings

Patch fixes sparse warnings: using plain integer as NULL pointer. Replaces
equal to with logical not operator.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Richard Gong <richard.gong@intel.com>
Link: https://lore.kernel.org/r/1591193212-15082-1-git-send-email-richard.gong@linux.intel.com


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