[SCSI] sr: fix corrupt CD data after media change and delay

Reported-by: Geert Uytterhoeven <[e-mail]>

If you delay 30s or more before mounting a CD after inserting it then
the kernel has the wrong value for the CD size.

http://marc.info/?t=121276133000001

The problem is in sr_test_unit_ready(): the function eats unit
attentions without adjusting the sdev->changed status. This means
that when the CD signals changed media via unit attention, we can
ignore it. Fix by making sr_test_unit_ready() adjust the changed
status.

Tested-by: Geert Uytterhoeven <[e-mail]>
Cc: Stable Tree <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>

drivers/scsi/sr.c

···
 		the_result = scsi_execute_req(sdev, cmd, DMA_NONE, NULL,
 					      0, sshdr, SR_TIMEOUT,
 					      retries--);
+		if (scsi_sense_valid(sshdr) &&
+		    sshdr->sense_key == UNIT_ATTENTION)
+			sdev->changed = 1;
 
 	} while (retries > 0 &&
 		 (!scsi_status_is_good(the_result) ||