[PATCH] prom_find_machine_type typo breaks pSeries lpar boot

A typo in prom_find_machine_type from Ben's recent patch "ppc64: Fix
result code handling in prom_init" prevents pSeries LPAR systems from
booting.

Tested on a pSeries 570 and OpenPower 720 (both Power5 LPAR).

Signed-off-by: Nathan Lynch <ntl@pobox.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>