Btrfs: use args in the correct order for kcalloc in btrfsic_read_block

kcalloc is defined as:

  kcalloc(size_t n, size_t size, gfp_t flags)

Although this won't cause problems in practice, btrfsic_read_block()
uses kcalloc with n and size in the opposite order.
Reviewed-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NLiu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/check-integrity.c

@@ -1594,6 +1594,7 @@ static int btrfsic_read_block(struct btrfsic_state *state,
 {
 	unsigned int num_pages;
 	unsigned int i;
+	size_t size;
 	u64 dev_bytenr;
 	int ret;
 
@@ -1608,9 +1609,8 @@ static int btrfsic_read_block(struct btrfsic_state *state,
 
 	num_pages = (block_ctx->len + (u64)PAGE_SIZE - 1) >>
 		    PAGE_SHIFT;
-	block_ctx->mem_to_free = kcalloc(sizeof(*block_ctx->datav) +
-						sizeof(*block_ctx->pagev),
-					 num_pages, GFP_NOFS);
+	size = sizeof(*block_ctx->datav) + sizeof(*block_ctx->pagev);
+	block_ctx->mem_to_free = kcalloc(num_pages, size, GFP_NOFS);
 	if (!block_ctx->mem_to_free)
 		return -ENOMEM;
 	block_ctx->datav = block_ctx->mem_to_free;