sel4: change a error message into warning

This condition is non-fatal in the most cases, so leave it as a
diagnostic message.

repos/base-sel4/src/core/include/vm_space.h

@@ -386,8 +386,9 @@ class Genode::Vm_space
 				if (!_map_frame(from_phys + offset, to_virt + offset,
 				                cacheability, writable, executable,
 				                flush_support))
-					error("mapping failed ", Hex(from_phys + offset),
-					      " -> ", Hex(to_virt + offset));
+					warning("mapping failed ", Hex(from_phys + offset),
+					        " -> ", Hex(to_virt + offset), " ",
+					        !flush_support ? "core" : "");
 			}
 		}