mtd: spinand: fix NULL pointer dereference in spinand_support_vendor_ops()

mtd: spinand: fix NULL pointer dereference in spinand_support_vendor_ops()

The spinand_support_vendor_ops() helper unconditionally dereferences
info->vendor_ops. For chips that do not define vendor_ops, this pointer
is NULL, leading to a kernel panic during probe:

Unable to handle kernel NULL pointer dereference at virtual address
0000000000000008

Add a guard to return early when vendor_ops is NULL. This prevents the
crash and allows SPI NAND devices without vendor-specific operations to
be probed correctly.

Fixes: fbc7538782f8 ("mtd: spinand: List vendor specific operations and make sure they are supported")
Cc: stable@vger.kernel.org
Signed-off-by: Md Sadre Alam <quic_mdalam@quicinc.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>