rtc: rv3029: Clean up error handling in rv3029_eeprom_write()

We don't need both "ret" and "err" when they do the same thing.  All the
functions called here return zero on success or negative error codes.
It's more clear to return a literal zero at the end instead of
"return ret;"

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>