drm/komeda: Rename main engine clk name "mclk" to "aclk"

To avoid confusion, unify the driver main engine clk name "mclk" to
the spec name "aclk".

Signed-off-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>