[SCSI] qla2xxx: Defer enablement of RISC interrupts until ISP initialization completes.

Josip Rodin noted
(http://article.gmane.org/gmane.linux.ports.sparc/10152) the
driver oopsing during registration of an rport to the
FC-transport layer with a backtrace indicating a dereferencing of
an shost->shost_data equal to NULL.  David Miller identified a
small window in driver logic where this could happen:

    > Look at how the driver registers the IRQ handler before the host has
    > been registered with the SCSI layer.
    >
    > That leads to a window of time where the shost hasn't been setup
    > fully, yet ISRs can come in and trigger DPC thread events, such as
    > loop resyncs, which expect the transport area to be setup.
    >
    > But it won't be setup, because scsi_add_host() hasn't finished yet.
    >
    > Note that in Josip's crash log, we don't even see the
    >
    >         qla_printk(KERN_INFO, ha, "\n"
    >             " QLogic Fibre Channel HBA Driver: %s\n"
    >             "  QLogic %s - %s\n"
    >             "  ISP%04X: %s @ %s hdma%c, host#=%ld, fw=%s\n",
    >  ...
    >
    > message yet.
    >
    > Which means that the crash occurs between qla2x00_request_irqs()
    > and printing that message.

Close this window by enabling RISC interrupts after the host has
been registered with the SCSI midlayer.

Reported-by: Josip Rodin <joy@entuzijast.net>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>