dt-bindings: power: supply: max8903: specify flt-gpios as input

The FLT pin was incorrected documented as an output. The MAX8903 uses it to
signal to the processor that a charging fault has occurred.

Signed-off-by: Herman van Hazendonk <github.com@herrie.org>
Link: https://lore.kernel.org/r/20240415151645.1986014-1-github.com@herrie.org
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>