orangefs: initialize op on loop restart in orangefs_devreq_read

In orangefs_devreq_read, there is a loop which picks an op off the list
of pending ops.  If the loop fails to find an op, there is nothing to
read, and it returns EAGAIN.  If the op has been given up on, the loop
is restarted via a goto.  The bug is that the variable which the found
op is written to is not reinitialized, so if there are no more eligible
ops on the list, the code runs again on the already handled op.

This is triggered by interrupting a process while the op is being copied
to the client-core.  It's a fairly small window, but it's there.

Signed-off-by: Martin Brandenburg <martin@omnibond.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>