ARM: dts: stm32: Set {bitclock,frame}-master phandles on DHCOM SoM

Fix the following dtbs_check warning:
arch/arm/boot/dts/stm32mp157c-dhcom-pdk2.dt.yaml: codec@a: port:endpoint@0:frame-master: True is not of type 'array'
arch/arm/boot/dts/stm32mp157c-dhcom-pdk2.dt.yaml: codec@a: port:endpoint@0:bitclock-master: True is not of type 'array'

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Cc: kernel@dh-electronics.com
Cc: linux-stm32@st-md-mailman.stormreply.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>