drm/v3d: Fix return if scheduler initialization fails

If the scheduler initialization fails, GEM initialization must fail as
well. Therefore, if `v3d_sched_init()` fails, free the DMA memory
allocated and return the error value in `v3d_gem_init()`.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240923141348.2422499-4-mcanal@igalia.com