msm: clock: Don't update clk->parent in clk_set_parent()

Any change to the parent field has to be done between __clk_pre_reparent()
and __clk_post_reparent() to avoid race conditions. So, stop setting the
parent field and leave it to the ops->set_parent() implementations to
update the parent field. All current implementations of ops->set_parent()
already do so.

Change-Id: Idc41bee306881a885335ecb322a21509231048cc
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>