Don't create a fake mmap offset in exynos_drm_gem_dumb_map_offset. If
not, it will call drm_gem_create_mmap_offset whenever user requests
DRM_IOCTL_MODE_MAP_DUMB ioctl.
Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>