spirv: Add missing break

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Fixes: c6465fec ("spirv: add SpvCapabilityInt64Atomics")
CID: 1442555
(cherry picked from commit 9a918050)