mmc: mmci: make unexported functions static

Fix the following sparse warnings by making any functions not used
outsde the mmci.c driver static.

drivers/mmc/host/mmci.c:422:6: warning: symbol 'mmci_dma_release' was not declared. Should it be static?
drivers/mmc/host/mmci.c:430:6: warning: symbol 'mmci_dma_setup' was not declared. Should it be static?
drivers/mmc/host/mmci.c:465:5: warning: symbol 'mmci_prep_data' was not declared. Should it be static?
drivers/mmc/host/mmci.c:481:6: warning: symbol 'mmci_unprep_data' was not declared. Should it be static?
drivers/mmc/host/mmci.c:490:6: warning: symbol 'mmci_get_next_data' was not declared. Should it be static?
drivers/mmc/host/mmci.c:498:5: warning: symbol 'mmci_dma_start' was not declared. Should it be static?
drivers/mmc/host/mmci.c:533:6: warning: symbol 'mmci_dma_finalize' was not declared. Should it be static?
drivers/mmc/host/mmci.c:542:6: warning: symbol 'mmci_dma_error' was not declared. Should it be static?
drivers/mmc/host/mmci.c:951:6: warning: symbol 'mmci_variant_init' was not declared. Should it be static?
drivers/mmc/host/mmci.c:956:6: warning: symbol 'ux500v2_variant_init' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>