clover/spirv: Add missing break for SpvOpExecutionMode case.

Fix defect reported by Coverity Scan.

Missing break in switch (MISSING_BREAK)
unterminated_case: The case for value SpvOpExecutionMode is not
terminated by a 'break' statement.

Fixes: ee5b46fcfd ("clover/spirv: support CL_KERNEL_COMPILE_WORK_GROUP_SIZE")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7519>

src/gallium/frontends/clover/spirv/invocation.cpp

@@ -199,6 +199,7 @@ namespace {
             default:
                break;
             }
+            break;
 
          case SpvOpDecorate: {
             const auto id = get<SpvId>(inst, 1);