[SCSI] sr: fix test unit ready responses

Commit 210ba1d1724f5c4ed87a2ab1a21ca861a915f734 updated sr.c to use
the scsi_test_unit_ready() function.  Unfortunately, this has the
wrong characteristic of eating NOT_READY returns which sr.c relies on
for tray status.

Fix by rolling an internal sr_test_unit_ready() that doesn't do this.

Tested-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
diff --git a/drivers/scsi/sr.h b/drivers/scsi/sr.h
index 81fbc0b..1e144df 100644
--- a/drivers/scsi/sr.h
+++ b/drivers/scsi/sr.h
@@ -61,6 +61,7 @@
 int sr_audio_ioctl(struct cdrom_device_info *, unsigned int, void *);
 
 int sr_is_xa(Scsi_CD *);
+int sr_test_unit_ready(struct scsi_device *sdev, struct scsi_sense_hdr *sshdr);
 
 /* sr_vendor.c */
 void sr_vendor_init(Scsi_CD *);