LU-556: Fix config_log_find() in mgc_request.c

LU-556: Fix config_log_find() in mgc_request.c

This issue was imported by lu-411. Actually after checking
the code, I found we can make things a bit simpler.

Change-Id: Iad212782a5f0357b73014baf7766c77637fb47db
Signed-off-by: Jinshan Xiong <jay@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1168
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mikhail Pershin <tappro@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>