nvmem: core: fix cleanup after dev_set_name()

In the Linux kernel, the following vulnerability has been resolved:

nvmem: core: fix cleanup after dev_set_name()

If dev_set_name() fails, we leak nvmem->wp_gpio as the cleanup does not
put this. While a minimal fix for this would be to add the gpiod_put()
call, we can do better if we split device_register(), and use the
tested nvmem_release() cleanup code by initialising the device early,
and putting the device.

This results in a slightly larger fix, but results in clear code.

Note: this patch depends on "nvmem: core: initialise nvmem->id early"
and "nvmem: core: remove nvmem_config wp_gpio".

[Srini: Fixed subject line and error code handing with wp_gpio while applying.]