hfsplus: Push down BKL into ioctl function

HFS is one of the remaining users of the ->ioctl function, convert it
blindly to unlocked_ioctl by pushing down the BKL.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>