ARM: only warn if unknown memory types are being mapped.

This is a workaround for missing writecombine & friends support. Needs
proper fixing, but too many other things to do atm to focus on that...

src/system/kernel/arch/arm/arch_vm.cpp

@@ -97,8 +97,8 @@ arch_vm_unset_memory_type(VMArea *area)
 status_t
 arch_vm_set_memory_type(VMArea *area, phys_addr_t physicalBase, uint32 type)
 {
-	if (type == 0)
-		return B_OK;
+	if (type != 0)
+		dprintf("%s: undefined type %lx!\n", __PRETTY_FUNCTION__, type);
 
-	return B_ERROR;
+	return B_OK;
 }