[SCSI] scsi: add wrapper functions for sg buffer copy helper functions

LLDs need to copies data between the SG table in struct scsi_cmnd and
liner buffer. So they use the helper functions like

sg_copy_from_buffer(scsi_sglist(sc), scsi_sg_count(sc), buf, buflen)
sg_copy_to_buffer(scsi_sglist(sc), scsi_sg_count(sc), buf, buflen)

This patch just adds wrapper functions:

scsi_sg_copy_from_buffer(sc, buf, buflen)
scsi_sg_copy_to_buffer(sc, buf, buflen)
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

include/scsi/scsi_cmnd.h

@@ -175,4 +175,18 @@ static inline struct scsi_data_buffer *scsi_out(struct scsi_cmnd *cmd)
 	return &cmd->sdb;
 }
 
+static inline int scsi_sg_copy_from_buffer(struct scsi_cmnd *cmd,
+					   void *buf, int buflen)
+{
+	return sg_copy_from_buffer(scsi_sglist(cmd), scsi_sg_count(cmd),
+				   buf, buflen);
+}
+
+static inline int scsi_sg_copy_to_buffer(struct scsi_cmnd *cmd,
+					 void *buf, int buflen)
+{
+	return sg_copy_to_buffer(scsi_sglist(cmd), scsi_sg_count(cmd),
+				 buf, buflen);
+}
+
 #endif /* _SCSI_SCSI_CMND_H */