misc: microchip: pci1xxxx: Fix some NULL vs IS_ERR() bugs

The devm_nvmem_register() function returns error pointers.  It never
returns NULL.  Update the checks accordingly.

Fixes: 09690015 ("misc: microchip: pci1xxxx: Add support to read and write into PCI1XXXX OTP via NVMEM sysfs")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/043df330-222b-4c2c-ae19-ed2f731bfe0b@moroto.mountain


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>