Clarify that images cannot be created from AHB with AHARDWAREBUFFER_FORMAT_BLOB (#1477)

Change-Id: I4aa8c2b1fbfb871ecc9e8b1d657dfd6c1e27481e

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

Author: kpet

api/opencl_runtime_layer.asciidoc

@@ -2331,7 +2331,7 @@ endif::cl_khr_external_memory[]
     ** if there are no devices in _context_ that support _image_format_
 ifdef::cl_khr_external_memory_android_hardware_buffer[]
     ** if _properties_ includes an AHardwareBuffer external memory handle and
-    the AHardwareBuffer format is not supported
+    the AHardwareBuffer format is `AHARDWAREBUFFER_FORMAT_BLOB` or not supported
 endif::cl_khr_external_memory_android_hardware_buffer[]
   * {CL_MEM_OBJECT_ALLOCATION_FAILURE}
     ** if there is a failure to allocate memory for the image object