Correct duplicate key hits when theme is changed.

When the theme was changed, it added the signal callback
a new time causing the signal to be processed more than
once.

PTAP-49

Change-Id: I22ba3b8ae1a4d0f7507788d7419be8dd61f9314a
Signed-off-by: Eduardo Lima (Etrunko) <eduardo.lima@intel.com>