ARM: OMAP: dmtimer: check for pm_runtime_get_sync() failure

The current OMAP dmtimer probe does not check for the return
status of pm_runtime_get_sync() before initializing the timer
registers. Any timer with missing hwmod data would return a
failure here, and the access of registers without enabling the
clocks for the timer would trigger a l3_noc interrupt and a
kernel boot hang. Add proper checking so that the probe would
return a failure graciously without hanging the kernel boot.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>