[SCSI] mptspi: fix oops in mptspi_dv_renegotiate_work()

The problem here is that if the ioc faults too early in the bring up
sequence (as it usually does for an irq routing problem), ioc_reset gets
called before the scsi host is even allocated.  This causes an oops when
it later schedules a renegotiation.  Fix this by checking ioc->sh before
trying to renegotiate.

Cc: "Moore, Eric" <Eric.Moore@lsi.com>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>