w1: Drop dm.h header file

This header file should not be included in other header files. Remove it
and use a forward declaration instead.

Signed-off-by: Simon Glass <sjg@chromium.org>

cmd/w1.c

@@ -6,6 +6,7 @@
  */
 #include <common.h>
 #include <command.h>
+#include <dm.h>
 #include <w1.h>
 #include <w1-eeprom.h>
 #include <dm/device-internal.h>