avr32: Fix typo of IFSR in a comment in the PIO header file

Signed-off-by: NHans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Signed-off-by: NHaavard Skinnemoen <haavard.skinnemoen@atmel.com>

arch/avr32/mach-at32ap/pio.h

@@ -57,7 +57,7 @@
 
 /* Bitfields in IFDR */
 
-/* Bitfields in ISFR */
+/* Bitfields in IFSR */
 
 /* Bitfields in SODR */