[SCSI] mpt2sas: Kernel Panic during Large Topology discovery

There was a configuration page timing out during the initial port
enable at driver load time. The port enable would fail, and this would
result in the driver unloading itself, meanwhile the driver was accessing
freed memory in another context resulting in the panic.  The fix is to
prevent access to freed memory once the driver had issued the diag reset
which woke up the sleeping port enable process.  The routine
_base_reset_handler was reorganized so the last sleeping process woken up was
the port_enable.

Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Cc: stable@kernel.org
Signed-off-by: James Bottomley <James.Bottomley@suse.de>