LU-1445 lod: clean up lod_fld_lookup() return codes

LU-1445 lod: clean up lod_fld_lookup() return codes

Don't return "rc" when it is known that this will always be "0".
This confuses the reader into thinking that this is an error path
when it is in fact a no-op shortcut that returns success.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: Ie4571226b3e90c866b958cf6ab65f6077abcab07
Reviewed-on: http://review.whamcloud.com/12727
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>