kfifo: fix sparse complaints

This patch fix complaints by the sparse tool when using kfifo_put() with
non scalar types like structures (i.e.
drivers/iio/industrialio-event.c).

Casting a pointer to the value and read this pointer instead of directly
casting the value will fix this.

The generated code is equal.
Signed-off-by: NStefani Seibold <stefani@seibold.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/kfifo.h

@@ -401,7 +401,7 @@ __kfifo_int_must_check_helper( \
 			((typeof(__tmp->type))__kfifo->data) : \
 			(__tmp->buf) \
 			)[__kfifo->in & __tmp->kfifo.mask] = \
-				(typeof(*__tmp->type))__val; \
+				*(typeof(__tmp->type))&__val; \
 			smp_wmb(); \
 			__kfifo->in++; \
 		} \