kwbimage: Fix check variable of checksum

calc_hdrcsum two times are checked. checksumi of exthdr is not checked.
Signed-off-by: NNobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
CC: Prafulla Wadaskar <prafulla@marvell.com>

tools/kwbimage.c

@@ -356,7 +356,7 @@ static int kwbimage_verify_header (unsigned char *ptr, int image_size,
 
 	calc_exthdrcsum = kwbimage_checksum8 ((void *)exthdr,
 			sizeof(extbhr_t) - sizeof(uint8_t), 0);
-	if (calc_hdrcsum != mhdr->checkSum)
+	if (calc_exthdrcsum != exthdr->checkSum)
 		return -FDT_ERR_BADSTRUCTURE; /* exthdr csum not matched */
 
 	return 0;