mtd: plat-ram: correctly free memory on error path in platram_probe()

If an error happens in mtd_device_parse_register or mtd_device_register,
memory allocated for struct platram_info is leaked.

Make platram_probe() call platram_remove() on all error paths
after struct platram_info allocation to correctly free resources.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Baskov Evgeiny <baskov@ispras.ru>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20201113160537.899-1-baskov@ispras.ru