selftests: breakpoints: Fix a typo of function name

Since commit 5821ba96 ("selftests: Add test plan API to kselftest.h
and adjust callers") accidentally introduced 'a' typo in the front of
run_test() function, breakpoint_test_arm64.c became not able to be
compiled.

Remove the 'a' from arun_test().

Fixes: 5821ba96

 ("selftests: Add test plan API to kselftest.h and adjust callers")
Reported-by: Jun Takahashi <takahashi.jun_s@aa.socionext.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>