[SCSI] mpt fusion: fix up msi_enable in mpt_suspend

There's a problem with the combination of the upstream power
management fixes and the enabling of MSI by default in that the
suspend path still uses the global variable.  Convert it to check
ioc->msi_enable.

Cc: "Moore, Eric" <Eric.Moore@lsi.com>
Cc: "Prakash, Sathya" <sathya.prakash@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>