USB: FHCI: cq_get() should check kfifo_out()'s return value

Since commit 7acd72eb ("kfifo: rename
kfifo_put... into kfifo_in... and kfifo_get... into kfifo_out..."),
kfifo_out() is marked __must_check, and that causes gcc to produce
lots of warnings like this:

  CC      drivers/usb/host/fhci-mem.o
In file included from drivers/usb/host/fhci-hcd.c:34:
drivers/usb/host/fhci.h: In function 'cq_get':
drivers/usb/host/fhci.h:520: warning: ignoring return value of 'kfifo_out', declared with attribute warn_unused_result
...

This patch fixes the issue by properly checking the return value.
Signed-off-by: Anton Vorontsov <avorontsov@mvista.com>
Cc: stable <stable@kernel.org> [.33 and .34]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/host/fhci.h

@@ -20,6 +20,7 @@
 
 #include <linux/kernel.h>
 #include <linux/types.h>
+#include <linux/bug.h>
 #include <linux/spinlock.h>
 #include <linux/interrupt.h>
 #include <linux/kfifo.h>
@@ -515,9 +516,13 @@ static inline int cq_put(struct kfifo *kfifo, void *p)
 
 static inline void *cq_get(struct kfifo *kfifo)
 {
-	void *p = NULL;
+	unsigned int sz;
+	void *p;
+
+	sz = kfifo_out(kfifo, (void *)&p, sizeof(p));
+	if (sz != sizeof(p))
+		return NULL;
 
-	kfifo_out(kfifo, (void *)&p, sizeof(p));
 	return p;
 }