staging/lustre/ptlrpc: Suppress error for flock requests

-EAGAIN is a normal return when requesting POSIX flocks.
We can't recognize exactly that case here, but it's the
only case that should result in -EAGAIN on LDLM_ENQUEUE, so
don't print to console in that case.

Signed-off-by: Patrick Farrell <paf@cray.com>
Reviewed-on: http://review.whamcloud.com/22856
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8658


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>