shared/gatt-client: Fix freeing instance while processing notification

shared/gatt-client: Fix freeing instance while processing notification

If CCC fails to be programmed the callback would be run without taking
a reference which may lead to freeing the client instance while there
are still notification to be processed.

To fix this handling of both success and failure to program the CCC will
now take a reference to the client, also in case of failure instead of
attempting to program the CCC once again the code now notify all the
queued requests which is consistent with how the success case is
handled.

Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>