drm/v3d: Drop allocation of object without mountpoint

Function drm_gem_shmem_create_with_mnt() creates an object
without using the mountpoint if gemfs is NULL.

Drop the else branch calling drm_gem_shmem_create().

Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241029-v3d-v2-1-c0d3dd328d1b@gmail.com