[SCSI] hpsa: fixup MSI-X registration

Commit 254f796b updated
the driver to use 16 MSI-X vectors, despite the fact that
older controllers would provide only 4.
This was causing MSI-X registration to drop down to INTx
mode. But as the controller support performant mode, the
initialisation will become confused and cause the machine
to stall during boot.

This patch fixes up the MSI-X registration to re-issue
the pci_enable_msix() call with the correct number of
MSI-X vectors. With that the hpsa driver continues to
works on older controllers like the P200.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Acked-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>