The SCSI_BNX2_ISCSI kconfig symbol selects CNIC and CNIC selects UIO, which
depends on MMU.

Since 'select' does not follow dependency chains, add the same MMU
dependency to SCSI_BNX2_ISCSI.

Quietens this kconfig warning:

WARNING: unmet direct dependencies detected for CNIC
  Depends on [n]: NETDEVICES [=y] && ETHERNET [=y] && NET_VENDOR_BROADCOM [=y] && PCI [=y] && (IPV6 [=m] || IPV6 [=m]=n) && MMU [=n]
  Selected by [m]:
  - SCSI_BNX2_ISCSI [=m] && SCSI_LOWLEVEL [=y] && SCSI [=y] && NET [=y] && PCI [=y] && (IPV6 [=m] || IPV6 [=m]=n)

Link: https://lore.kernel.org/r/20201129070916.3919-1-rdunlap@infradead.org
Fixes: cf4e6363 ("[SCSI] bnx2i: Add bnx2i iSCSI driver.")
Cc: linux-scsi@vger.kernel.org
Cc: Nilesh Javali <njavali@marvell.com>
Cc: Manish Rangankar <mrangankar@marvell.com>
Cc: GR-QLogic-Storage-Upstream@marvell.com
Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>