dcache: d_find_alias needn't recheck IS_ROOT && DCACHE_DISCONNECTED

If we get to this point and discover the dentry is not a root dentry, or
not DCACHE_DISCONNECTED--great, we always prefer that anyway.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>