[SCSI] scsi_host_lookup: error returns and NULL pointers

This patch cleans up the behavior of scsi_host_lookup().

The original implementation attempted to use the dual role of
either returning a pointer value, or a negative error code.
User's needed to use IS_ERR() to check the result. Additionally,
the IS_ERR() macro never checks for when a NULL pointer was
returned, so a NULL pointer actually passes with a success case.
Note: scsi_host_get(), used by scsi_host_lookup(), can return
a NULL pointer.

Talk about a mudhole for the unitiated to step into....

This patch converts scsi_host_lookup() to return either NULL
or a valid pointer. The consumers were updated for the change.

Signed-off-by: James Smart <james.smart@emulex.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/hosts.c

@@ -464,7 +464,7 @@ static int __scsi_host_match(struct device *dev, void *data)
 struct Scsi_Host *scsi_host_lookup(unsigned short hostnum)
 {
 	struct device *cdev;
-	struct Scsi_Host *shost = ERR_PTR(-ENXIO);
+	struct Scsi_Host *shost = NULL;
 
 	cdev = class_find_device(&shost_class, NULL, &hostnum,
 				 __scsi_host_match);