SystemUi UsbDialog: fix label vulnerability

Change loadLabel to loadSafeLabel

Test: atest SystemUITests:UsbConfirmActivityTest
Test: atest SystemUITests:UsbPermissionActivityTest
Flag: android.hardware.usb.flags.enable_persistent_usb_device_permissions
Bug: 472968114
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:89ea066ba92f262d2e0be0f2c3eee5669101ebb5
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:ac097ce019fce7696b2889b2f53b02fac059db09
Merged-In: Ied6847d3c9761a976ddbb85bf7618c48793b4069
Change-Id: Ied6847d3c9761a976ddbb85bf7618c48793b4069