ARM: dts: use ti,fixed-factor-clock for dpll4_m4x2_mul_ck

We need to use set-rate-parent for dpll4_m4 clock path, so use the
ti,fixed-factor-clock version which supports set-rate-parent property.

The set-rate-parent flag itself is set in the following patch, this one
just changes the clock driver to ti,fixed-factor-clock without any other
changes.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Tested-by: Christoph Fritz <chf.fritz@googlemail.com>
Tested-by: Marek Belisko <marek@goldelico.com>
Acked-by: Tony Lindgren <tony@atomide.com>