x86, olpc: fix model detection without OFW

Impact: fix "garbled display, laptop is unusable" bug

Commit e51a1ac2 ("x86, olpc: fix endian
bug in openfirmware workaround") breaks model comparison on OLPC; the value
0xc2 needs to be scaled up by olpc_board().

The pre-patch version was wrong, but accidentally worked anyway
(big-endian 0xc2 is big enough to satisfy all other board revisions,
but little endian 0xc2 is not).

Signed-off-by: Chris Ball <cjb@laptop.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Andres Salomon <dilinger@queued.net>
Cc: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>