drbd: fifo_alloc() should use struct_size

Switching to struct_size for the allocation in fifo_alloc avoids
hard-coding the type of fifo_buffer.values in fifo_alloc. It also
provides overflow protection; to avoid pessimistic code being
generated by the compiler as a result, this patch also switches
fifo_size to unsigned, propagating the change as appropriate.

Reviewed-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index ddbf560..aae99a2 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -622,7 +622,7 @@ struct fifo_buffer {
 	int total; /* sum of all values */
 	int values[0];
 };
-extern struct fifo_buffer *fifo_alloc(int fifo_size);
+extern struct fifo_buffer *fifo_alloc(unsigned int fifo_size);
 
 /* flag bits per connection */
 enum {