e1000e: release hw semaphore after successfully writing EEPROM

Since e1000e has been existance in linux-2.6, we've
never released the hardware semaphore after a successful
write to the SPI EEPROM.  I guess we don't write to
SPI EEPROM much -- but those few of us that do appreciate
it when we can later read from the EEPROM without having
to reboot.

Found-by: Nick Van Fossen <Nick.VanFossen@riverbed.com>
Signed-off-by: Arthur Jones <ajones@riverbed.com>
Reviewed-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>