omap: Keep nwires for omap1 and 2420 MMC controller

A patch from Sukumar Ghorai <s-ghorai@ti.com> changed the
nwires to use caps instead. However, nwires is still
needed for the earlier controller.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Sukumar Ghorai <s-ghorai@ti.com>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>