libgui: reset buffer count to max slots instead of returning BAD_VALUE.

CRs-Fixed: 3013293

Change-Id: Idfafcd6aa718054ff749bd5d1c7eb2630be0f109
Signed-off-by: DennySPb <dennyspb@gmail.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Simao Gomes Viana <simao@halogenos.org>
Signed-off-by: Simão Gomes Viana <devel@superboring.dev>