thermal_mgmt: Fix undefined error for fwk_thread_put_event

Recently fwk_thread_put_event function is been renamed to
fwk_put_event. However one instance of this is not updated
in mod_thermal_mgmt.c. This commit fixes this.

Change-Id: I81ce475b3e0b54abcaf8e7b1177733cb0e22b16f
Signed-off-by: Girish Pathak <girish.pathak@arm.com>