[natsemi] Convert stray mmio readl() to pio inl()

This driver uses programmed I/O to access hardware registers.  There is
a stray memory-mapped I/O read on a programmed I/O address.  Perhaps
this is an artifact of porting the driver.  Fix this by converting it to
programmed I/O.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Marty Connor <mdc@etherboot.org>

src/drivers/net/natsemi.c

         wcsr = inl (np->ioaddr + WOLCmd) & WCSR_RESET_SAVE;
 
         /* RFCR */
-        rfcr = readl (np->ioaddr + RxFilterAddr) & RFCR_RESET_SAVE;
+        rfcr = inl (np->ioaddr + RxFilterAddr) & RFCR_RESET_SAVE;
 
         /* PMATCH */
         for (i = 0; i < 3; i++) {