signal/arm64: Better isolate the COMPAT_TASK portion of ptrace_hbptriggered

Instead of jumpping while !is_compat_task placee all of the code
inside of an if (is_compat_task) block.  This allows the int i
variable to be properly limited to the compat block no matter how the
rest of ptrace_hbptriggered changes.

In a following change a non-variable declaration will preceed
was made independent to ensure the code is easy to review.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>