m68k: amiga: Use str_plural() to fix Coccinelle warning

Fixes the following Coccinelle/coccicheck warning reported by
string_choices.cocci:

	opportunity for str_plural(zorro_num_autocon)

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20240412215704.204403-4-thorsten.blum@toblux.com


Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>