[U-Boot] mmc: add function prototype for mmc_set_dev in mmc.h

[Steve Sakoman <steve@sakoman.com>]

this eliminates compiler warnings when cmd_mmc.c is built with CONFIG_SYS_MMC_SET_DEV

the mmc_set_dev implementation in omap3_mmc.c is also tweaked to match
the new prototype in parameter naming and type

Signed-off-by: Steve Sakoman <steve@sakoman.com>
---

diff --git a/drivers/mmc/omap3_mmc.c b/drivers/mmc/omap3_mmc.c
index 4eda216..9506cca 100644
--- a/drivers/mmc/omap3_mmc.c
+++ b/drivers/mmc/omap3_mmc.c
@@ -55,9 +55,9 @@ mmc_card_data cur_card_data;
 static block_dev_desc_t mmc_blk_dev;
 static hsmmc_t *mmc_base = (hsmmc_t *)OMAP_HSMMC1_BASE;
 
-unsigned char mmc_set_dev(int dev)
+int mmc_set_dev(int dev_num)
 {
-	switch (dev) {
+	switch (dev_num) {
 	case 1:
 		mmc_base = (hsmmc_t *)OMAP_HSMMC1_BASE;
 		break;
diff --git a/include/mmc.h b/include/mmc.h
index 8973bc7..fcb237e 100644
--- a/include/mmc.h
+++ b/include/mmc.h
@@ -271,6 +271,7 @@ int mmc_initialize(bd_t *bis);
 int mmc_init(struct mmc *mmc);
 int mmc_read(struct mmc *mmc, u64 src, uchar *dst, int size);
 struct mmc *find_mmc_device(int dev_num);
+int mmc_set_dev(int dev_num);
 void print_mmc_devices(char separator);
 int board_mmc_getcd(u8 *cd, struct mmc *mmc);