imximage: header.length of 4 is valid

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
diff --git a/tools/imximage.c b/tools/imximage.c
index 0da48a7..7e60bf5 100644
--- a/tools/imximage.c
+++ b/tools/imximage.c
@@ -361,8 +361,8 @@
 	dcd_v2_t *dcd_v2 = &hdr_v2->dcd_table;
 	uint32_t size, version;
 
-	size = be16_to_cpu(dcd_v2->header.length) - 8;
-	if (size > (MAX_HW_CFG_SIZE_V2 * sizeof(dcd_addr_data_t))) {
+	size = be16_to_cpu(dcd_v2->header.length);
+	if (size > (MAX_HW_CFG_SIZE_V2 * sizeof(dcd_addr_data_t)) + 8) {
 		fprintf(stderr,
 			"Error: Image corrupt DCD size %d exceed maximum %d\n",
 			(uint32_t)(size / sizeof(dcd_addr_data_t)),