Fix endianness before touching DMA controller

QEMU sends us a little endian length, the DMA controller expects big
endian.

Bug: 122111962
Change-Id: I9a1f587bcaa7b845ed499716cd7c6324bcd9d776
diff --git a/test-runner/arm64/boot.c b/test-runner/arm64/boot.c
index 94cb2d5..aaf23ec 100644
--- a/test-runner/arm64/boot.c
+++ b/test-runner/arm64/boot.c
@@ -87,7 +87,7 @@
      * Both are big-endian so byte order reversal is needed.
      */
     *cfg_ctl = rev16(FW_CFG_KERNEL_SIZE);
-    dma.length = *cfg_data32;
+    dma.length = rev32(*cfg_data32);
     if (!dma.length) {
         /* Return if no image was provided */
         return;