mfd: Make asic3_clk_enable() a void function

The return value of asic3_clk_enable() was neither used nor useful. So let's
make it a void function, and thereby match asic3_clk_disable().

Signed-off-by: Paul Parsons <lost.distance@yahoo.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>