ptp: ocp: handle error from nvmem_device_find

nvmem_device_find returns a valid pointer or IS_ERR().
Handle this properly.

Fixes: 0cfcdd1e ("ptp: ocp: add nvmem interface for accessing eeprom")
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Link: https://lore.kernel.org/r/20220329160354.4035-1-jonathan.lemon@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>