[SCSI] wd33c93: fix up cut and paste error

The three drivers: a2091, gvp11 and mvme147 have erroneous references
to a3000_host.  Fix these to be references to the proper host
variable.

Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>