cmd: bootm: fix build when CONFIG_CMD_IMLS_NAND

Now when CONFIG_CMD_IMLS_NAND is enabled the u-boot build will fail,
because nand_read_skip_bad() function has been changed to accept more
parameters, hence fix it.

 CC      cmd/bootm.o
cmd/bootm.c: In function 'nand_imls_legacyimage':
cmd/bootm.c:390:8: error: too few arguments to function 'nand_read_skip_bad'
  ret = nand_read_skip_bad(mtd, off, &len, imgdata);
        ^
In file included from cmd/bootm.c:18:0:
include/nand.h:101:5: note: declared here
 int nand_read_skip_bad(struct mtd_info *mtd, loff_t offset, size_t *length,
     ^
 LD      drivers/block/built-in.o

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>