jfs: fix array-index-out-of-bounds read in add_missing_indices

In the Linux kernel, the following vulnerability has been resolved: jfs: fix array-index-out-of-bounds read in add_missing_indices stbl is s8 but it must contain offsets into slot which can go from 0 to 127. Added a bound check for that error and return -EIO if the check fails. Also make jfs_readdir return with error if add_missing_indices returns with an error.