scsi: core: Minor comment fixes for scsi_host_busy()

scsi: core: Minor comment fixes for scsi_host_busy()

I guess that the @shost comment on scsi_host_busy() was copied from
scsi_host_get() (as it is the same), however they do not do the same
thing.

Also drop reference to busy counter, which has been removed.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20251023082759.3927000-1-john.g.garry@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>