Fix a bug in snp driver binding Start() that it may return incorrect status code.

Signed-off-by: Ari Zigler <ariz@mellanox.com>
Reviewed-by: Ye Ting  <ting.ye@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14115 6f19259b-4bc3-4df7-8a09-765794883524