LU-3474 mdd: mdd_links_read() to return linkea_init() errors

LU-3474 mdd: mdd_links_read() to return linkea_init() errors

ASSERTION(ldata->ld_leh != ((void *)0)) can be triggered in
linkea_links_find() due to earlier mdd_links_read() call
missing to return linkea_init() errors and thus preventing
to detect that ld_leh is not populated.
Plus a few error handling fixes to avoid unnecessary msgs
and also prevent early return.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I35b1076d8eb036dd600e0fda711417634590b9df
Reviewed-on: http://review.whamcloud.com/6676
Tested-by: Hudson
Reviewed-by: wangdi <di.wang@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>