Properly release partial wakelock during SRVCC

When an active call was moved from IMS->GsmCdma using
SRVCC, the partial wakelock was not released, causing
the device to stay awake during the call.

This change properly releases the wakelock in this
condition.

Bug: 117747831
Test: atest FrameworksTelephonyTests
Change-Id: I6d8f706afc1adadf4198586c4f39dbe8065df58b