mmc: prevent some warnings with make W=1

Add missing prototypes for global functions and
make local functions static.

cc: panto@antoniou-consulting.com
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
diff --git a/drivers/mmc/omap_hsmmc.c b/drivers/mmc/omap_hsmmc.c
index 17cbb09..5b0c302 100644
--- a/drivers/mmc/omap_hsmmc.c
+++ b/drivers/mmc/omap_hsmmc.c
@@ -120,7 +120,7 @@
 }
 #endif
 
-unsigned char mmc_board_init(struct mmc *mmc)
+static unsigned char mmc_board_init(struct mmc *mmc)
 {
 #if defined(CONFIG_OMAP34XX)
 	t2_t *t2_base = (t2_t *)T2_BASE;