mmc: mxcmmc: Fix MODULE_ALIAS

The correct name for the driver is "mxc-mmc".

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Chris Ball <cjb@laptop.org>