Fix markup in cl_img_safety_mechanisms extension (KhronosGroup#1424)

Change-Id: I0f9c12e034a611b6acc8c6de60b9c7f47d89188c

Signed-off-by: Kevin Petit <kevin.petit@arm.com>

Author: kpet

extensions/cl_img_safety_mechanisms.asciidoc

@@ -163,6 +163,7 @@ Devices that set `CL_DEVICE_QUEUE_SUPPORTED` for `CL_DEVICE_WORKGROUP_PROTECTION
   If `CL_CONTEXT_WORKGROUP_PROTECTION_IMG` is specified, all kernel commands enqueued to this context will enable error checking at the workgroup level to verify that all memory operations within each workgroup workgroup perform as expected. This may effect performance. This property requires the `cl_img_workgroup_protection` extension to be present.
 
   If `CL_CONTEXT_ENHANCED_EVENT_EXECUTION_STATUS_IMG` is specified, additional event execution status' will be available. This property requires the `cl_img_enhanced_event_execution_status` extension to be present.
+|====
 --
 
 (Modify Section 5.11, *Event Objects*) ::