gfs2: Simplify function gfs2_upgrade_iopen_glock

When trying to upgrade the iopen glock, gfs2_upgrade_iopen_glock() tries
to take the iopen glock with the LM_FLAG_TRY_1CB flag set before trying
to take it without the LM_FLAG_TRY or LM_FLAG_TRY_1CB flags set.  Both
calls will cause the lock contention bast callbacks to be invoked
throughout the cluster, and we really don't need them to be invoked
twice.  Remove the first LM_FLAG_TRY_1CB call to eliminate unnecessary
dlm traffic.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>