fix sysvfs symlinks

The thing got broken back in 2002 - sysvfs does *not* have inline
symlinks; even short ones have bodies stored in the first block
of file.  sysv_symlink() handles that correctly; unfortunately,
attempting to look an existing symlink up will end up confusing
them for inline symlinks, and interpret the block number containing
the body as the body itself.

Nobody has noticed until now, which says something about the level
of testing sysvfs gets ;-/

Cc: stable@vger.kernel.org # all of them, not that anyone cared
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>