qcom: soc: pil-q6v5: Explicitly set GFMUX source

Don't assume the GFMUX register is untouched by another process,
explicitly set the 2-bit field for source select.

Change-Id: Ic688fcb836a932c648707458096364c9a8305a70
Acked-by: Jennifer L. Zenner <jzenner@qti.qualcomm.com>
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>