IB/srp: Avoid that sg_reset -d ${srp_device} triggers an infinite loop

commit ee92efe4 upstream.

Use different loop variables for the inner and outer loop. This avoids
that an infinite loop occurs if there are more RDMA channels than
target->req_ring_size.

Fixes: d92c0da7 ("IB/srp: Add multichannel support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>