avr32: fix use of non-existing portnr variable in at32_map_usart()

This patch fixes the use of the non-existing portnr variable in
at32_map_usart() to use the provided line number instead. Typo was introduced
in commit 2b348e2f.
Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>

arch/avr32/mach-at32ap/at32ap700x.c

@@ -1044,7 +1044,7 @@ void __init at32_map_usart(unsigned int hw_id, unsigned int line, int flags)
 	}
 
 	pdata = pdev->dev.platform_data;
-	pdata->num = portnr;
+	pdata->num = line;
 	at32_usarts[line] = pdev;
 }