mmc: fix cb710 kconfig dependency warning

Fix kconfig dependency warning to satisfy dependencies:

  warning: (MMC_CB710 && MMC && PCI) selects CB710_CORE which has
  unmet direct dependencies (MISC_DEVICES && PCI)

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Chris Ball <cjb@laptop.org>