pinctrl: renesas: rzg2l: Fix invalid unsigned return in rzg3s_oen_read()

pinctrl: renesas: rzg2l: Fix invalid unsigned return in rzg3s_oen_read()

rzg3s_oen_read() returns a u32 value, but previously propagated a negative
error code from rzg3s_pin_to_oen_bit(), resulting in an unintended large
positive value due to unsigned conversion. This caused incorrect
output-enable reporting for certain pins.

Without this patch, pins P1_0-P1_4 and P7_0-P7_4 are incorrectly reported
as "output enabled" in the pinconf-pins debugfs file. With this fix, only
P1_0-P1_1 and P7_0-P7_1 are shown as "output enabled", which matches the
hardware manual.

Fix this by returning 0 when the OEN bit lookup fails, treating the pin
as output-disabled by default.

Fixes: a9024a323af2 ("pinctrl: renesas: rzg2l: Clean up and refactor OEN read/write functions")
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20250709160819.306875-2-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>