btrfs: free pages on error in btrfs_uring_read_extent()

In the Linux kernel, the following vulnerability has been resolved: btrfs: free pages on error in btrfs_uring_read_extent() In this function the 'pages' object is never freed in the hopes that it is picked up by btrfs_uring_read_finished() whenever that executes in the future. But that's just the happy path. Along the way previous allocations might have gone wrong, or we might not get -EIOCBQUEUED from btrfs_encoded_read_regular_fill_pages(). In all these cases, we go to a cleanup section that frees all memory allocated by this function without assuming any deferred execution, and this also needs to happen for the 'pages' allocation.