MAINTAINERS: Add file patterns for scsi device tree bindings

Submitters of device tree binding documentation may forget to CC the
subsystem maintainer if this is missing.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: James E.J. Bottomley <jejb@linux.vnet.ibm.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>