compat_ioctl: simplify calling of handlers

The compat_ioctl array now contains only entries for ioctl numbers
that do not require a separate handler. By special-casing the
ULONG_IOCTL case in the do_ioctl_trans function, we can kill the
final use of a function pointer in the array.

   text    data     bss     dec     hex filename
   7539   13352    2080   22971    59bb before/fs/compat_ioctl.o
   7910    8552    2080   18542    486e after/fs/compat_ioctl.o

Signed-off-by: Arnd Bergmann <arnd@arndb.de>