Report recoverable errors as warnings

At present many recoverable failures are reported as errors. This patch
modifies all such failures to be reported as warnings instead.

Change-Id: I5141653c82498defcada9b90fdf7498ba496b2f2
diff --git a/drivers/io/io_memmap.c b/drivers/io/io_memmap.c
index 0809973..40b8e9a 100644
--- a/drivers/io/io_memmap.c
+++ b/drivers/io/io_memmap.c
@@ -137,7 +137,7 @@
 		entity->info = (uintptr_t)&current_file;
 		result = IO_SUCCESS;
 	} else {
-		ERROR("A Memmap device is already active. Close first.\n");
+		WARN("A Memmap device is already active. Close first.\n");
 		result = IO_RESOURCES_EXHAUSTED;
 	}