IntelFrameworkModulePkg: Avoid key notification called more than once

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=996

Issue:
In current code logic, when a key is pressed, it will search
the whole NotifyList to find whether a notification has been
registered with the keystroke. if yes, it will en-queue the
key for notification execution later. And now if different
notification functions have been registered with the same key,
then the key will be en-queued more than once. Then it will
cause the notification executed more than once.

This patch is to enhance the code logic to fix this issue.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>

IntelFrameworkModulePkg/Csm/BiosThunk/KeyboardDxe/BiosKeyboard.c

@@ -1986,6 +1986,7 @@ BiosKeyboardTimerHandler (
       //
       Enqueue (&BiosKeyboardPrivate->QueueForNotify, &KeyData);
       gBS->SignalEvent (BiosKeyboardPrivate->KeyNotifyProcessEvent);
+      break;
     }
   }