soc: qcom: dfc: Ignore grants after powersave

If rmnet receives a grant after going into powersave, the start grant
will be incorrect when coming out of powersave. And if this grant is 0
then data stall will happen.

This change ignores any grant received after rmnet enters powersave.

Change-Id: I45dbfaa28b23806584d5a47738e7a87f76ead889
Acked-by: Weiyi Chen <weiyic@qti.qualcomm.com>
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>