btrfs: use struct fscrypt_str instead of struct qstr

[ Upstream commit 6db75318 ]

While struct qstr is more natural without fscrypt, since it's provided
by dentries, struct fscrypt_str is provided by the fscrypt handlers
processing dentries, and is thus more natural in the fscrypt world.
Replace all of the struct qstr uses with struct fscrypt_str.

Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Stable-dep-of: 9af86694 ("btrfs: file_remove_privs needs an exclusive lock in direct io write")
Signed-off-by: Sasha Levin <sashal@kernel.org>