btrfs: move priv off stack in btrfs_encoded_read_regular_fill_pages()

btrfs: move priv off stack in btrfs_encoded_read_regular_fill_pages()

[ Upstream commit 68d3b27e05c7ca5545e88465f5e2be6eda0e11df ]

Change btrfs_encoded_read_regular_fill_pages() so that the priv struct
is allocated rather than stored on the stack, in preparation for adding
an asynchronous mode to the function.

Signed-off-by: Mark Harmstone <maharmstone@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Stable-dep-of: 05b36b04d74a ("btrfs: fix use-after-free in btrfs_encoded_read_endio()")
Signed-off-by: Sasha Levin <sashal@kernel.org>