When I2C=m and SPI=y or-ing them will produce =y while
what we need is the lower bound, i.e. =m.  Fortunately
SPI is a boolean so we need to handle only one special
case.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Jakub Kicinski <kubakici@wp.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>