bpf: switch fdget_raw() uses to CLASS(fd_raw, ...)

Swith fdget_raw() use cases in bpf_inode_storage.c to CLASS(fd_raw).

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>