omap4: pandaboard: Fix the init if CONFIG_MMC_OMAP_HS is not set

Avoid possible crash if CONFIG_MMC_OMAP_HS is not set.

Signed-off-by: David Anders <x0132446@ti.com>
Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>