ARM: dts: AM43x-epos: Fix clk parent for synctimer

commit 55ee7017 ("arm: omap2: board-generic: use omap4_local_timer_init
for AM437x") makes synctimer32k as the clocksource on AM43xx. By default
the synctimer32k is clocked by 32K RTC OSC on AM43xx. But this 32K RTC OSC
is not available on epos boards which makes it fail to boot.

Synctimer32k can also be clocked by a peripheral PLL, so making this as
clock parent for synctimer3k on epos boards.

Fixes: 55ee7017 ("arm: omap2: board-generic: use omap4_local_timer_init for AM437x")
Cc: stable@vger.kernel.org # v4.4+
Reported-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>