bloblist: Rename the SPL tag

Add a U_BOOT prefix to this tag since it is specific to the U-Boot
project.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl.c b/common/spl/spl.c
index 4c101ec..f51d1f3 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -408,7 +408,7 @@
 {
 	struct spl_handoff *ho;
 
-	ho = bloblist_ensure(BLOBLISTT_SPL_HANDOFF, sizeof(struct spl_handoff));
+	ho = bloblist_ensure(BLOBLISTT_U_BOOT_SPL_HANDOFF, sizeof(struct spl_handoff));
 	if (!ho)
 		return -ENOENT;
 
@@ -425,7 +425,7 @@
 	struct spl_handoff *ho;
 	int ret;
 
-	ho = bloblist_find(BLOBLISTT_SPL_HANDOFF, sizeof(struct spl_handoff));
+	ho = bloblist_find(BLOBLISTT_U_BOOT_SPL_HANDOFF, sizeof(struct spl_handoff));
 	if (!ho)
 		return -ENOENT;
 	handoff_save_dram(ho);