From: "Randy.Dunlap" <rddunlap@osdl.org>

We need to call mca_system_init() to register MCA bus struct, otherwise
find_mca_adapter() oopses with a NULL ptr dereference.

Fixes this oops reported last week:
	http://marc.theaimsgroup.com/?l=linux-kernel&m=108455738606747&w=2

Thanks to James Bottomley for pointing this out.