drm: writeback: Fix drm_writeback_connector_cleanup signature

drm: writeback: Fix drm_writeback_connector_cleanup signature

The drm_writeback_connector_cleanup have the signature:

     static void drm_writeback_connector_cleanup(
		struct drm_device *dev,
		struct drm_writeback_connector *wb_connector)

But it is stored and used as a drmres_release_t

    typedef void (*drmres_release_t)(struct drm_device *dev, void *res);

While the current code is valid and does not produce any warning, the
CFI runtime check (CONFIG_CFI_CLANG) can fail because the function
signature is not the same as drmres_release_t.

In order to fix this, change the function signature to match what is
expected by drmres_release_t.

Fixes: 1914ba2b91ea ("drm: writeback: Create drmm variants for drm_writeback_connector initialization")
Suggested-by: Mark Yacoub <markyacoub@google.com>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Link: https://lore.kernel.org/r/20250429-drm-fix-writeback-cleanup-v2-1-548ff3a4e284@bootlin.com
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>