ARM: entry: prefetch abort helper: pass aborted pc in r4 rather than r0

This avoids unnecessary instructions for CPUs which implement the IFAR
(instruction fault address register).

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/pabort-v7.S

@@ -4,7 +4,7 @@
 /*
  * Function: v6_pabort
  *
- * Params  : r0 = address of aborted instruction
+ * Params  : r4 = address of aborted instruction
  *
  * Returns : r0 = address of abort
  *	   : r1 = IFSR