IB/srp: Handle partial connection success correctly

Avoid that the following kernel warning is reported if the SRP
target system accepts fewer channels per connection than what
was requested by the initiator system:

WARNING: at drivers/infiniband/ulp/srp/ib_srp.c:617 srp_destroy_qp+0xb1/0x120 [ib_srp]()
Call Trace:
[<ffffffff8105d67f>] warn_slowpath_common+0x7f/0xc0
[<ffffffff8105d6da>] warn_slowpath_null+0x1a/0x20
[<ffffffffa05419e1>] srp_destroy_qp+0xb1/0x120 [ib_srp]
[<ffffffffa05445fb>] srp_create_ch_ib+0x19b/0x420 [ib_srp]
[<ffffffffa0545257>] srp_create_target+0x7d7/0xa94 [ib_srp]
[<ffffffff8138dac0>] dev_attr_store+0x20/0x30
[<ffffffff812079ef>] sysfs_write_file+0xef/0x170
[<ffffffff81191fc4>] vfs_write+0xb4/0x130
[<ffffffff8119276f>] sys_write+0x5f/0xa0
[<ffffffff815a0a59>] system_call_fastpath+0x16/0x1b

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Sebastian Parschauer <sebastian.riemer@profitbricks.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Signed-off-by: Doug Ledford <dledford@redhat.com>