drm/msm/dpu: Cleanup callers of dpu_hw_blk_init

Outside of superfluous parameter checks the dpu_hw_blk_init()
doesn't have any failure paths. Switch it over to be a void
function and we can remove error handling paths in all the functions
that call it. While we're in those functions remove unneeded
initialization for a static variable.

v3: No changes
v2: Removed a cleanup intended for a different patch

Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>