Minor warnings in Keil pack v1.1.0

[jlj-ee]

In my current project using the Keil pack version of the MSDK drivers (v1.1.0), Keil's compiler throws two minor warnings from the driver code:

A quick scan of the code currently in the repo suggests that the first warning has already been fixed here on GitHub, but the second warning would still be raised from the MXC_SYS_RTCClockDisable declaration in mxc_sys.h across all targets.

Very low priority but fixing this would be a nice QoL for a future pack release