clocksource: versatile: Use sched_clock_register()

The newly merged versatile sched clock support uses a deprecated
interface.  Of course that patch got routed through the ARM tree instead
of going through the relevant maintainer tree.

Use the proper interface so we can get rid of the cruft.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>