scsi: mesh: Stop using struct scsi_pointer

scsi: mesh: Stop using struct scsi_pointer

This driver doesn't use SCp.ptr to save a SCSI command data pointer which
means "scsi pointer" is a complete misnomer here. Only a few members of
struct scsi_pointer are used and the rest waste memory.  Avoid the "struct
foo { struct bar; };" silliness.

Link: https://lore.kernel.org/r/fbf930e64af5b15ca028dfe25b00fe933951f19b.1645484982.git.fthain@linux-m68k.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>