ARM: dts: stm32: Fix LED5 on STM32MP1 DHCOM PDK2

On the prototype DHCOM, the LED5 was connected to pin PG2 of the
STM32MP15xx, however on the production SoM this was changed to pin
PC6. Update the connection in the DT.

Fixes: 81d5fc71 ("ARM: dts: stm32: Add GPIO LEDs for STM32MP1 DHCOM PDK2")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: linux-stm32@st-md-mailman.stormreply.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>