fs/9p: destroy fid on failed remove

9P spec says:
"It is correct to consider remove to be a clunk with the
side effect of removing the file if permissions allow. "

So even if remove fails we need to destroy the fid.

Without this patch an rmdir on a directory with contents leave
the new cloned directory fid fid attached to fidlist. On umount
we dump the fids on the fidlist

~# rmdir /mnt2/test4/
rmdir: failed to remove `/mnt2/test4/': Directory not empty
~# umount /mnt2/
~# dmesg
[  228.474323] Found fid 3 not clunked

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>