mfd: Modifying the twl4030-power macro name Main_Ref to all caps

Modifying the macro name Main_Ref to all caps(MAIN_REF).

Suggested by Nishanth Menon <nm@ti.com>

Signed-off-by: Lesly A M <leslyam@ti.com>
Cc: Nishanth Menon <nm@ti.com>
Cc: David Derrick <dderrick@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>