mmc: mmci: Fix compiler error when CONFIG_OF is not set

error: implicit declaration of function 'mmci_dt_populate_generic_pdata'

This is due to the '#if CONFIG_OF' guards placed around
mmci_dt_populate_generic_pdata(), but not around the call to it. We
repair this by inserting a stub which elegantly returns when CONFIG_OF
is not set.

Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>