tools, rsa: Further minor cleanups on top of c236ebd and 2b9ec7

[NOTE: I took v1 of these patches in, and then v2 came out, this commit
is squashing the minor deltas from v1 -> v2 of updates to c236ebd and
2b9ec76 into this commit - trini]

- Added an additional NULL check, as suggested by Simon Glass to
  fit_image_process_sig
- Re-formatted the comment blocks

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Simon Glass <sjg@chromium.org>
[For merging the chnages from v2 back onto v1]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/tools/image-host.c b/tools/image-host.c
index 399ec94..1104695 100644
--- a/tools/image-host.c
+++ b/tools/image-host.c
@@ -238,11 +238,16 @@
 	/* Get keyname again, as FDT has changed and invalidated our pointer */
 	info.keyname = fdt_getprop(fit, noffset, "key-name-hint", NULL);
 
-	ret = info.algo->add_verify_data(&info, keydest);
+	if (keydest)
+		ret = info.algo->add_verify_data(&info, keydest);
+	else
+		return -1;
 
-	/* Write the public key into the supplied FDT file; this might fail
+	/*
+	 * Write the public key into the supplied FDT file; this might fail
 	 * several times, since we try signing with successively increasing
-	 * size values */
+	 * size values
+	 */
 	if (keydest && ret)
 		return ret;