alpha: add $(src)/ rather than $(obj)/ to make source file path

commit 5ed78e5523fd9ba77b8444d380d54da1f88c53fc upstream.

$(ev6-y)divide.S is a source file, not a build-time generated file.
So, it should be prefixed with $(src)/ rather than $(obj)/.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>