mtd: rawnand: Add a check in of_get_nand_secure_regions()

Check for whether of_property_count_elems_of_size() returns a negative
error code.

Fixes: 13b89768 ("mtd: rawnand: Add support for secure regions in NAND memory")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/YMtQFXE0F1w7mUh+@mwanda