i915: Fix gem_context_has_engine_map() for older kernels

CI is currently breaking on linus/drm-intel-fixes due to the assert that
the kernel supports context engine maps. Report the lack of maps on
older kernels gracefully!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>

lib/i915/gem_engine_topology.c

@@ -321,10 +321,13 @@ bool gem_context_has_engine_map(int fd, uint32_t ctx)
 		.param = I915_CONTEXT_PARAM_ENGINES,
 		.ctx_id = ctx
 	};
-	int ret;
 
-	ret = __gem_context_get_param(fd, &param);
-	igt_assert_eq(ret, 0);
+	/*
+	 * If the kernel is too old to support PARAM_ENGINES,
+	 * then naturally the context has no engine map.
+	 */
+	if (__gem_context_get_param(fd, &param))
+		return false;
 
 	return param.size;
 }