mtd: physmap_of: Fix resources leak in 'of_flash_probe()'

If 'of_flash_probe_gemini()' or 'of_flash_probe_versatile()' fail, we must
reslease some resources, as already done in all error handling paths in
this function.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>