ARM: dts: Fix wrong mdio clock for dm814x

Recent PTP-specific cpsw driver changes started exposing an issue on at
at least j5eco-evm:

Unhandled fault: external abort on non-linefetch (0x1008) at 0xf0169004
...
(davinci_mdio_runtime_suspend) from [<c063f2a4>] (__rpm_callback+0x84/0x154)
(__rpm_callback) from [<c063f394>] (rpm_callback+0x20/0x80)
(rpm_callback) from [<c063f4f0>] (rpm_suspend+0xfc/0x6ac)
(rpm_suspend) from [<c0640af0>] (pm_runtime_work+0x88/0xa4)
(pm_runtime_work) from [<c0155338>] (process_one_work+0x228/0x568)
...

Let's fix the issue by using the correct mdio clock as suggested by
Grygorii Strashko <grygorii.strashko@ti.com>.

The DM814_ETHERNET_CPGMAC0_CLKCTRL clock is the interconnect target module
clock and managed by ti-sysc.

Fixes: 6398f347

 ("ARM: dts: Configure interconnect target module for dm814x cpsw")
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>