mtd: maps: physmap: Return -ENOMEM directly when info allocation fails

There's no point going to the err_out path since no resources have
been allocated yet, just return -ENOMEM directly.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>