scsi: target: tcmu: Rename TCM_DEV_BIT_PLUGGED to TCMU_DEV_BIT_PLUGGED

The bit definition TCM_DEV_BIT_PLUGGED should correctly be named
TCMU_DEV_BIT_PLUGGED, since all other bits in the same bitfield have prefix
TCMU_.

Link: https://lore.kernel.org/r/20210512140654.31249-1-bostroesser@gmail.com


Signed-off-by: Bodo Stroesser <bostroesser@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>