msm:ipa: unvote PCIe clock only if it was voted before

this fix makes sure to unvote PCIE clock only if it was voted before
from the same function.

Change-Id: Ie4060b7c54598ef7aa1b8b4a4a8f06d2067d2542
Signed-off-by: Michael Adisumarta <madisuma@codeaurora.org>