test: fix sparse warnings in user_copy tests

test: fix sparse warnings in user_copy tests

Sparse fix for "test: check copy_to/from_user boundary validation":

To keep sparse happy with the horrible things being done with the user
memory pointers, declare both __user and non-__user cases ahead of time to
avoid needing to do the casts later.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>