zorro: Make sysfs config attribute read-only

zorro: Make the sysfs `config' attribute read-only, as you cannot write to it
(there's no .write function neither).

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>