clk: davinci: pll-dm355: fix SYSCLKn parent names

This fixes the parent clock names of the SYSCLKn clocks for the DM355
SoC in the TI DaVinici PLL clock driver.

It appears that this name just didn't get updated to the correct name
like the other SoCs during the driver's development.

Reported-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: David Lechner <david@lechnology.com>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20180525181150.17873-3-david@lechnology.com