Adjust fbd_list() definition to avoid clang 15 warning

With clang 15, the following -Werror warnings is produced:

    sys/dev/fb/fbd.c:205:9: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
    fbd_list()
            ^
             void

This is because fbd_list() is declared with a (void) argument list, but
defined with an empty argument list. Make the definition match the
declaration.

MFC after:	3 days

sys/dev/fb/fbd.c

@@ -202,7 +202,7 @@ fb_init(struct fb_list_entry *entry, int unit)
 }
 
 int
-fbd_list()
+fbd_list(void)
 {
 	struct fb_list_entry *entry;