mtd: rawnand: Fix probe failure due to of_get_nand_secure_regions()

mtd: rawnand: Fix probe failure due to of_get_nand_secure_regions()

Due to 14f97f0b8e2b, the rawnand platforms without "secure-regions"
property defined in DT fails to probe. The issue is,
of_get_nand_secure_regions() errors out if
of_property_count_elems_of_size() returns a negative error code.

If the "secure-regions" property is not present in DT, then also we'll
get -EINVAL from of_property_count_elems_of_size() but it should not
be treated as an error for platforms not declaring "secure-regions"
in DT.

So fix this behaviour by checking for the existence of that property in
DT and return 0 if it is not present.

Fixes: 14f97f0b8e2b ("mtd: rawnand: Add a check in of_get_nand_secure_regions()")
Reported-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Martin Kaiser <martin@kaiser.cx>
Tested-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210727062813.32619-1-manivannan.sadhasivam@linaro.org