thermal: gov_user_space: Do not lock thermal zone mutex

Commit 670a5e35 ("thermal/core: Move the thermal zone lock out of
the governors") moved thermal zone locking away from governors, but it
forgot about the user space one which deadlocks now.

Fix this by removing the thermal zone locking from the user space
governor.

Fixes: 670a5e35 ("thermal/core: Move the thermal zone lock out of the governors")
Tested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>