staging: vchiq_2835_arm: quit using custom down_interruptible()

vchi_killable.h overrides down_interruptible() by implementing a
function similar to down_killable(). To make things simpler we turn
calls to down_interruptible() into kernel's implementation of
down_killable().
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c

@@ -543,7 +543,7 @@ create_pagelist(char __user *buf, size_t count, unsigned short type)
 		(g_cache_line_size - 1)))) {
 		char *fragments;
 
-		if (down_interruptible(&g_free_fragments_sema) != 0) {
+		if (down_killable(&g_free_fragments_sema)) {
 			cleanup_pagelistinfo(pagelistinfo);
 			return NULL;
 		}