m68k/mac: Export Peripheral System Controller (PSC) base address to modules

If CONFIG_MACMACE=m:

    ERROR: psc [drivers/net/ethernet/apple/macmace.ko] undefined!

Add the missing export to fix this.
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/m68k/mac/psc.c

@@ -29,6 +29,7 @@
 
 int psc_present;
 volatile __u8 *psc;
+EXPORT_SYMBOL_GPL(psc);
 
 /*
  * Debugging dump, used in various places to see what's going on.