Unlike i386, m68k get_thread_area has no arguments.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220602013401.303699-17-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>