drivers/ata/: make 4 functions static

This patch makes the following needlessly global functions static:
- libata-core.c: ata_qc_complete_internal()
- libata-scsi.c: ata_scsi_qc_new()
- libata-scsi.c: ata_dump_status()
- libata-scsi.c: ata_to_sense_error()

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Jeff Garzik <jeff@garzik.org>