fsdev: Fix overrun after readlink() fills buffer completely
readlink() returns the number of bytes written to the buffer, and it
doesn't write a terminating null byte. do_readlink() writes it
itself. Overruns the buffer when readlink() filled it completely.
Fix by reserving space for the null byte when calling readlink(), like
we do elsewhere.
Signed-off-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>