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

[Paulraj, Sandeep]

> Subject: 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 at sakoman.com>
> ---


Thanks 

pushed to u-boot-ti

Sandeep