ext4: fix potential memory leak in ext4_fc_record_modified_inode()

In the Linux kernel, the following vulnerability has been resolved: ext4: fix potential memory leak in ext4_fc_record_modified_inode() As krealloc may return NULL, in this case 'state->fc_modified_inodes' may not be freed by krealloc, but 'state->fc_modified_inodes' already set NULL. Then will lead to 'state->fc_modified_inodes' memory leak.