RDMA/iw_cxgb4: Fix incorrect function parameters

RDMA/iw_cxgb4: Fix incorrect function parameters

While reading the TCB field in t4_tcb_get_field32() the wrong mask is
passed as a parameter which leads the driver eventually to a kernel
panic/app segfault from access to an illegal SRQ index while flushing the
SRQ completions during connection teardown.

Fixes: 11a27e2121a5 ("iw_cxgb4: complete the cached SRQ buffers")
Link: https://lore.kernel.org/r/20200511185608.5202-1-bharat@chelsio.com
Signed-off-by: Potnuri Bharat Teja <bharat@chelsio.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>