arm64: dts: imx8mq-librem5: Bump BUCK1 suspend voltage up to 0.85V

arm64: dts: imx8mq-librem5: Bump BUCK1 suspend voltage up to 0.85V

The minimal voltage of VDD_SOC sourced from BUCK1 is 0.81V, which
is the currently set value. However, BD71837 only guarantees accuracy
of ±0.01V, and this still doesn't factor other reasons for actual
voltage to slightly drop in, resulting in the possibility of running
out of the operational range.

Bump the voltage up to 0.85V, which should give enough headroom.

Cc: stable@vger.kernel.org
Fixes: 8f0216b006e5 ("arm64: dts: Add a device tree for the Librem 5 phone")
Signed-off-by: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@puri.sm>
Signed-off-by: Frank Li <Frank.Li@nxp.com>