Fix ClipboardService device lock check for cross profile

ClipboardService.isDeviceLocked should clear callingIdentity before
accessing KeyguardManager.

Test: bit CtsDevicePolicyManagerTestCases:com.android.cts.devicepolicy.ManagedProfileTest

Bug: 64934810
Change-Id: I81a7adac8c9d56ed801ffc1380fcbc987d5df3e6
Merged-In: I712abfe8d542cd1be9c1816f407c8912321ac480