clk: msm: mdmfermium: Correct parent entry for gpll0_a_clk_src

Make xo_a_clk_src the parent for gpll0_a_clk_src. This should let
xo shoutdown to happen if no client other than cpu is using gpll0.

Change-Id: If38823f3a8ed5985c4fa0010f2799b0e63ca8c96
Signed-off-by: Jaydeep Sen <jsen@codeaurora.org>