uml: cow_user.c warning corrections

Fix this warning:

  arch/um/drivers/cow_user.c: In function `absolutize':
  arch/um/drivers/cow_user.c:189:7: warning: ignoring return value of `chdir', declared with attribute warn_unused_result

[richard@nod.at: happens only with -D_FORTIFY_SOURCE=2]
Signed-off-by: Vitaliy Ivanov <vitalivanov@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/drivers/cow_user.c

@@ -186,7 +186,11 @@ static int absolutize(char *to, int size, char *from)
 		strcat(to, "/");
 		strcat(to, from);
 	}
-	chdir(save_cwd);
+	if (chdir(save_cwd)) {
+		cow_printf("absolutize : Can't cd to '%s' - "
+			   "errno = %d\n", save_cwd, errno);
+		return -1;
+	}
 	return 0;
 }