media: use size_t for integer iterator to Vector::size()

Change-Id: I0a744dc7815a86a993df9b0623440be620ec8903
diff --git a/media/mtp/MtpDevice.cpp b/media/mtp/MtpDevice.cpp
index 1df7af9..d6d5dd5 100644
--- a/media/mtp/MtpDevice.cpp
+++ b/media/mtp/MtpDevice.cpp
@@ -195,7 +195,7 @@
 
 MtpDevice::~MtpDevice() {
     close();
-    for (unsigned int i = 0; i < mDeviceProperties.size(); i++)
+    for (size_t i = 0; i < mDeviceProperties.size(); i++)
         delete mDeviceProperties[i];
     usb_request_free(mRequestIn1);
     usb_request_free(mRequestIn2);
@@ -253,7 +253,7 @@
             ALOGI("*** FORMAT: %s\n", MtpDebug::getFormatCodeName(format));
             MtpObjectPropertyList* props = getObjectPropsSupported(format);
             if (props) {
-                for (unsigned int j = 0; j < props->size(); j++) {
+                for (size_t j = 0; j < props->size(); j++) {
                     MtpObjectProperty prop = (*props)[j];
                     MtpProperty* property = getObjectPropDesc(prop, format);
                     if (property) {