mtd: ssfdc: One function call less in ssfdcr_add_mtd() after error detection

The kfree() function was called in one case by
the ssfdcr_add_mtd() function during error handling
even if the passed data structure member contained a null pointer.
This issue was detected by using the Coccinelle software.

Thus use another label.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/56d92e42-db9e-4767-bcb1-9686bdf34a03@web.de