net: aquantia: Fix for missing atl_unlock_fw()

Fix atl_update_thermal_flag() to not return from the function without
calling atl_unlock_fw() when thermal monitoring is not supported by
the firmware.

Change-Id: I39fec668f75a67187772f8cc5df08f183d2b6a0f
Signed-off-by: Jinesh K. Jayakumar <jineshk@codeaurora.org>