arm64: dts: mediatek: mt6357: Drop regulator-fixed compatibles

arm64: dts: mediatek: mt6357: Drop regulator-fixed compatibles

Some of the regulators in the MT6357 PMIC dtsi have compatible set to
regulator-fixed, even though they don't serve any purpose: all those
regulators are handled as a whole by the mt6357-regulator driver. In
fact this is the only dtsi in this family of chips where this is the
case: mt6359 and mt6358 don't have any such compatibles.

A side-effect caused by this is that the DT kselftest, which is supposed
to identify nodes with compatibles that can be probed, but haven't,
shows these nodes as failures.

Remove the useless compatibles to move the dtsi in line with the others
in its family and fix the DT kselftest failures.

Fixes: 55749bb478f8 ("arm64: dts: mediatek: add mt6357 device-tree")
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/r/20250502-mt6357-regulator-fixed-compatibles-removal-v1-1-a582c16743fe@collabora.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>