Include 'dw_mmc-pltfm.h' header file in order to fix the following
sparse warnings:

drivers/mmc/host/dw_mmc-pltfm.c:36:5: warning: symbol 'dw_mci_pltfm_register' was not declared. Should it be static?
drivers/mmc/host/dw_mmc-pltfm.c:94:1: warning: symbol 'dw_mci_pltfm_pmops' was not declared. Should it be static?
drivers/mmc/host/dw_mmc-pltfm.c:118:5: warning: symbol 'dw_mci_pltfm_remove' was not declared. Should it be static?
Suggested-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJingoo Han <jg1.han@samsung.com>
Acked-by: NSeungwon Jeon <tgih.jun@samsung.com>
Signed-off-by: NChris Ball <cjb@laptop.org>