mtd: fix compiler warnings

- add missing declaration
- update debug output format specifiers

Signed-off-by: Steve Rae <steve.rae@raedomain.com>

include/linux/mtd/mtd.h

@@ -500,5 +500,10 @@ int mtd_arg_off(const char *arg, int *idx, loff_t *off, loff_t *size,
 int mtd_arg_off_size(int argc, char *const argv[], int *idx, loff_t *off,
 		     loff_t *size, loff_t *maxsize, int devtype,
 		     uint64_t chipsize);
+
+/* drivers/mtd/mtdcore.c */
+void mtd_get_len_incl_bad(struct mtd_info *mtd, uint64_t offset,
+			  const uint64_t length, uint64_t *len_incl_bad,
+			  int *truncated);
 #endif
 #endif /* __MTD_MTD_H__ */