scsi: megaraid: Fix ifnullfree.cocci warnings

NULL check before vfree is not needed.

Generated by: scripts/coccinelle/free/ifnullfree.cocci

Link: https://lore.kernel.org/r/alpine.DEB.2.22.394.2012111113060.2669@hadrien
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: kernel test robot <lkp@intel.com>
Signed-off-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>