arm/omap: Replace board_ref_clock with enum values

Use the enum for board_ref_clock from linux/wl12xx.h

Signed-off-by: Vikram Narayanan <vikram186@gmail.com>
Cc: linux-omap@vger.kernel.org
Reviewed-by: Pankaj <Jangra&lt;jangra.pankaj9@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>