xirc2ps_cs: fix register access when enabling FullDuplex

The current code incorrectly passes (XIRCREG1_ECR | FullDuplex) as
the register address to GetByte(), instead of fetching the register
value and OR-ing it with FullDuplex. This results in an invalid
register access.

Fix it by reading XIRCREG1_ECR first, then or-ing with FullDuplex
before writing it back.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Alok Tiwari <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Reviewed-by: Jacob Keller <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/xircom/xirc2ps_cs.c

···
 	    msleep(40);			/* wait 40 msec to let it complete */
 	}
 	if (full_duplex)
-	    PutByte(XIRCREG1_ECR, GetByte(XIRCREG1_ECR | FullDuplex));
+	    PutByte(XIRCREG1_ECR, GetByte(XIRCREG1_ECR) | FullDuplex);
     } else {  /* No MII */
 	SelectPage(0);
 	value = GetByte(XIRCREG_ESR);	 /* read the ESR */