OMAP2/3: mmc-twl4030: use correct controller in twl_mmc23_set_power

twl_mmc23_set_power() has MMC2 twl_mmc_controller hardcoded in it, which
breaks MMC3. Find the right controller to use instead.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>