mediatek: fit: fix use of uninitialized variable

mediatek: fit: fix use of uninitialized variable

When building the kernel with -Wmaybe-uninitialized, GCC reports this
warning:

block/partitions/fit.c: In function 'parse_fit_partitions':
block/partitions/fit.c:164:3: warning: 'images' may be used uninitialized in this function [-Wmaybe-uninitialized]
  164 |   printk(KERN_ERR "FIT: Cannot find %s node: %d\n", FIT_CONFS_PATH, images);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It appears to be a copy paste error. It's the "config" variable that is
supposed to be printed.

Fixes: e6aac8d98f56 ("image: add support for building FIT image with filesystem")
Signed-off-by: Qingfang Deng <qingfang.deng@siflower.com.cn>