display: remove compiler warnings

Use correct typecasts and format specifiers and resolve
compiler warnings

Change-Id: I51b12ecb78a9a496cf1f76c3d32892a203f70c43
diff --git a/libexternal/external.cpp b/libexternal/external.cpp
index 98a22cd..bf82cd8 100644
--- a/libexternal/external.cpp
+++ b/libexternal/external.cpp
@@ -191,7 +191,7 @@
         return;
     } else {
         len = read(hdmiScanInfoFile, scanInfo, sizeof(scanInfo)-1);
-        ALOGD("%s: Scan Info string: %s length = %zu",
+        ALOGD("%s: Scan Info string: %s length = %zd",
                  __FUNCTION__, scanInfo, len);
         if (len <= 0) {
             close(hdmiScanInfoFile);
@@ -313,7 +313,7 @@
         return false;
     } else {
         len = read(hdmiEDIDFile, edidStr, sizeof(edidStr)-1);
-        ALOGD_IF(DEBUG, "%s: EDID string: %s length = %zu",
+        ALOGD_IF(DEBUG, "%s: EDID string: %s length = %zd",
                  __FUNCTION__, edidStr, len);
         if ( len <= 0) {
             ALOGE("%s: edid_modes file empty '%s'",