[PATCH] powerpc: Fix typo in powermac platform functions

New sparse caught that typo which could have caused erratic hardware
behaviour on some machines if the platform functions are used by the
firmware to change bits in some FCR registers.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>