bugfix imgtool verify()

Signed-off-by: Christian Skubich <christian@skubware.de>
diff --git a/scripts/imgtool/main.py b/scripts/imgtool/main.py
index 5ed4daa..d5bf89f 100755
--- a/scripts/imgtool/main.py
+++ b/scripts/imgtool/main.py
@@ -116,12 +116,14 @@
         return
     elif ret == image.VerifyResult.INVALID_MAGIC:
         print("Invalid image magic; is this an MCUboot image?")
-    elif ret == image.VerifyResult.INVALID_MAGIC:
+    elif ret == image.VerifyResult.INVALID_TLV_INFO_MAGIC:
         print("Invalid TLV info magic; is this an MCUboot image?")
     elif ret == image.VerifyResult.INVALID_HASH:
         print("Image has an invalid sha256 digest")
     elif ret == image.VerifyResult.INVALID_SIGNATURE:
         print("No signature found for the given key")
+    else:
+        print("Unknown return code: {}".format(ret))
     sys.exit(1)