Revert "drm/msm: dpu: Use clk-name instead of assigned clk name"

This reverts commit 41a8e886.

This reversion is happening as a result of disabling the
disp/dpu directory as it will not be used in 4.19 downstream
display driver and these changes are made in the common layer
which affects the downstream driver functionalities. Separate
patches are submitted to revert the upstream driver and
introduce the downstream version of display driver.

Change-Id: Ic85675fe3c824e02775f594571aaa6853b9d6cbe
Signed-off-by: Samantha Tran <samtran@codeaurora.org>