cifs: handle cache lookup errors different than -ENOENT

lookup_cache_entry() might return an error different than -ENOENT
(e.g. from ->char2uni), so handle those as well in
cache_refresh_path().

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>