Replaced instances of toUpperCase() with uppercase() as the former is now deprecated and will cause errors when updating to future Kotlin releases.

Bug: 237017037

Test: Ran `atest DeskClockTests` after implementing the above fix and received the following results:

Summary (Test executed with 1 devices.)
-------
arm64-v8a DeskClockTests: Passed: 68, Failed: 0, Ignored: 0, Assumption
Failed: 0,

Change-Id: I2cf9b950b6bdcbd38a07c2a1a5dc13dce5391c79
3 files changed