input: redefine INPUT_COMPAT_TEST as in_compat_syscall()

The input compat code should work like all other compat code: for 32-bit
syscalls, use the 32-bit ABI and for 64-bit syscalls, use the 64-bit
ABI.  We have a helper for that (in_compat_syscall()): just use it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>