drm/vc4: plane: fix inconsistent indenting warning

Fix below inconsistent indenting smatch warning.
smatch warnings:
drivers/gpu/drm/vc4/vc4_plane.c:2083 vc6_plane_mode_set() warn: inconsistent indenting

Signed-off-by: Charles Han <hanchunchao@inspur.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250305102107.2595-1-hanchunchao@inspur.com