firewire: use in_compat_syscall to check ioctl compatness

Firewire was using is_compat_task to check whether it was in a compat
ioctl or a non-compat ioctl.  Use is_compat_syscall instead so it works
properly on all architectures.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>