In ll_file_read() use (*ppos + count - 1) for end of read instead of the value

In ll_file_read() use (*ppos + count - 1) for end of read instead of the value
in policy->l_extent.end.  This makes the intent of the comparison more clear,
and avoids any problems if the policy data is ever changed (e.g. to return the
granted extent or similar).

Useful debugging for lock extent problems.
b=2925