Fix non-ISA link error in drivers/scsi/advansys.c

When CONFIG_ISA is disabled, the isa_driver support will not be compiled
in.  Define stubs so that we don't get link-time errors.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>