um: get rid of pointless include "..." where include <...> will do

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/drivers/ubd_user.c b/arch/um/drivers/ubd_user.c
index ffe02c4..a703e45 100644
--- a/arch/um/drivers/ubd_user.c
+++ b/arch/um/drivers/ubd_user.c
@@ -19,7 +19,7 @@
 #include <byteswap.h>
 
 #include "ubd.h"
-#include "os.h"
+#include <os.h>
 
 void ignore_sigwinch_sig(void)
 {