IB/hfi1: Remove incorrect call to do_interrupt callback

The general interrupt handler is_rcv_avail_int() has two paths,
do_interrupt() (callback) and handle_user_interrupt().  The
do_interrupt() callback is for the threaded receive handling.
is_rcv_avail_int() cannot handle threaded IRQs.

If the do_interrupt() path is taken, and the IRQ returns
IRQ_WAKE_THREAD, the IRQ behavior will be indeterminate.

Remove incorrect call to do_interrupt() from is_rcv_avail_int(),
leaving the un-threaded (handle_user_interrupt()) path.

Fixes: f4f30031 ("staging/rdma/hfi1: Thread the receive interrupt.")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Kamenee Arumugam <kamenee.arumugam@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>