clk: ti: OMAP5: Correct the DT clock aliases for timers

The DT clock aliases for Timers use the legacy (non-DT) device
names and a source clock named sys_ck. OMAP5 is DT-boot only,
so correct the DT clock aliases to use the DT device names
instead. Also, the source clock name is corrected from 'sys_ck'
to 'timer_sys_ck', the name used by the OMAP dmtimer driver.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>