libsparse: fix crc chunk parsing in simg_dump.py

Change-Id: Ia5b7cedd88809b0e421a056704d25afa190470b8
diff --git a/libsparse/simg_dump.py b/libsparse/simg_dump.py
index 6ece31d..c70d45f 100755
--- a/libsparse/simg_dump.py
+++ b/libsparse/simg_dump.py
@@ -135,7 +135,7 @@
           break;
         else:
           crc_bin = FH.read(4)
-          crc = struct.unpack("<I", crc)
+          crc = struct.unpack("<I", crc_bin)
           print("Unverified CRC32 0x%08X" % (crc))
       else:
           print("Unknown chunk type 0x%04X" % (chunk_type), end="")