mmc: dw_mmc-socfpga: Staticize dw_mci_socfpga_probe

'dw_mci_socfpga_probe' is used only in this file. Make it static.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>