Properly check for Blob max length

sizeof(mBlob.value) is incorrect because writeBlob pads up to the next
AES_BLOCK_SIZE

Bug:22802399
Change-Id: I377edca2c7ea2cf4455f22f5f927fdad79893729

keystore/keystore.cpp

@@ -412,12 +412,12 @@ class Blob {
 public:
     Blob(const uint8_t* value, size_t valueLength, const uint8_t* info, uint8_t infoLength,
             BlobType type) {
-        if (valueLength > sizeof(mBlob.value)) {
-            valueLength = sizeof(mBlob.value);
+        if (valueLength > VALUE_SIZE) {
+            valueLength = VALUE_SIZE;
             ALOGW("Provided blob length too large");
         }
-        if (infoLength + valueLength > sizeof(mBlob.value)) {
-            infoLength = sizeof(mBlob.value) - valueLength;
+        if (infoLength + valueLength > VALUE_SIZE) {
+            infoLength = VALUE_SIZE - valueLength;
             ALOGW("Provided info length too large");
         }
         mBlob.length = valueLength;