scsi: mpi3mr: Get target object based on rphy

When device is registered with the STL then get the corresponding device's
target object using the rphy in below callback functions:

 - mpi3mr_target_alloc()

 - mpi3mr_slave_alloc()

 - mpi3mr_slave_configure()

 - mpi3mr_slave_destroy()

Link: https://lore.kernel.org/r/20220804131226.16653-11-sreekanth.reddy@broadcom.com
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>