Don't pass a user buffer pointer as the data pointer in a CCB.

Allocate a temporary buffer in the kernel to serve as the CCB data
pointer for a pass-through transaction and use copyin/copyout to
shuffle the data to/from the user buffer.

Reviewed by: scottl, brooks
Obtained from: CheriBSD
MFC after: 2 weeks
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D24489