e_backlight_main: fix compiling when not having Eeze

Summary:
EINA_UNUSED is defined in Eina. Since we are not using the program at all,
let's void main()'s arguments instead of trying to ignore them.

Test Plan: tested only on OSX, unbreaks the build.

Reviewers: zmike

Subscribers: cedric

Differential Revision: https://phab.enlightenment.org/D2387

src/bin/e_backlight_main.c

@@ -170,7 +170,7 @@ main(int argc, char **argv)
 }
 #else  // !HAVE_EEZE && !__FreeBSD_kernel__
 int
-main(int argc EINA_UNUSED, char **argv EINA_UNUSED)
+main(void)
 {
    return -1;
 }