Debugger: Fix number of appearances of data watch points

At least on Linux setting one data watch point resulted in two
view entries, since we parse two responses (direct command
response, and later GDB notification). Suppressing the second
was not working well enough.

Change-Id: Ica99c000d4912a9480a9e7020d2fdfdb866753b5
Reviewed-by: Christian Stenger <christian.stenger@digia.com>
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>