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 2b348e2f82f532e3aff8e0ce9293033b3294c1e0.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
diff --git a/arch/avr32/mach-at32ap/at32ap700x.c b/arch/avr32/mach-at32ap/at32ap700x.c
index aa677e2..1b7ad97 100644
--- a/arch/avr32/mach-at32ap/at32ap700x.c
+++ b/arch/avr32/mach-at32ap/at32ap700x.c
@@ -1044,7 +1044,7 @@
 	}
 
 	pdata = pdev->dev.platform_data;
-	pdata->num = portnr;
+	pdata->num = line;
 	at32_usarts[line] = pdev;
 }