io_uring/kbuf: kill dead struct io_buffer_list 'nr_entries' member

This is only ever assigned, never used. The only used part is the
calculated mask, which is used for indexing. Kill 'nr_entries'.

Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/kbuf.c

@@ -680,7 +680,6 @@ int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
 	}
 #endif
 
-	bl->nr_entries = reg.ring_entries;
 	bl->mask = reg.ring_entries - 1;
 	bl->flags |= IOBL_BUF_RING;
 	bl->buf_ring = br;

io_uring/kbuf.h

@@ -27,7 +27,6 @@ struct io_buffer_list {
 	__u16 bgid;
 
 	/* below is for ring provided buffers */
-	__u16 nr_entries;
 	__u16 head;
 	__u16 mask;