libata: make ata_print_id atomic

This variable is incremented from multiple contexts (module_init via
libata-lldds and the libsas discovery thread).  Make it atomic to head
off any chance of libsas and libata creating duplicate ids.

Acked-by: Jacek Danecki <jacek.danecki@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
index 2e26fca..9d0fd0b 100644
--- a/drivers/ata/libata.h
+++ b/drivers/ata/libata.h
@@ -53,7 +53,7 @@
 	ATA_DNXFER_QUIET	= (1 << 31),
 };
 
-extern unsigned int ata_print_id;
+extern atomic_t ata_print_id;
 extern int atapi_passthru16;
 extern int libata_fua;
 extern int libata_noacpi;