[SCSI] vmw_pvscsi: fix signedness warning with newer compilers

pvscsi_setup_msix() expects 'irq' argument to be an int but is being
passed unsigned int. Unsigned int is more proper type for IRQ number
so let's use it. This shuts off a compile warning with recent
compilers.

Signed-off-by: Dmitry Torokhov <dtor@vmware.com>
Acked-by: Alok Kataria <akataria@vmware.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>