tgsi: initialize Atomic field in tgsi_default_declaration

Spotted by Coverity.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/auxiliary/tgsi/tgsi_build.c

@@ -110,6 +110,7 @@ tgsi_default_declaration( void )
    declaration.Invariant = 0;
    declaration.Local = 0;
    declaration.Array = 0;
+   declaration.Atomic = 0;
    declaration.Padding = 0;
 
    return declaration;