fs/hfsplus: use bool instead of int for is_known_namespace() return value

is_known_namespace() only returns true/false.  Also remove inline and let
compiler decide what to do with static functions.

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>