clk: ti: DRA7: Correct timer_sys_ck clock aliases for Timers

The OMAP DMTimer API, omap_dm_timer_set_source(), can set the parent
of a timer node using 3 different values that use fixed parent names
for the clocks. The parent name, timer_sys_ck, is used for setting the
parent when used with the source index OMAP_TIMER_SRC_SYS_CLK. This
should point to the TIMER_SYS_CLK and not the SYSCLKIN2, so correct
the clock aliases appropriately. SYSCLKIN2 is not a mandatory clock
input.

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