mmc: add function prototype for mmc_set_dev in mmc.h

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>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
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_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);