Fix clang static analyzer warnings.

Fix the following warning:
frameworks/av/media/mtp/MtpServer.cpp:1098:5: warning: Assigned value is
garbage or undefined [clang-analyzer-core.uninitialized.Assign]

BUG:None
TEST:Warnings fixed.
Change-Id: If4e54ebd9b865e2e6cdc7666da0c9987a918df7c
diff --git a/media/mtp/MtpServer.cpp b/media/mtp/MtpServer.cpp
index 88dabff..b4947f8 100644
--- a/media/mtp/MtpServer.cpp
+++ b/media/mtp/MtpServer.cpp
@@ -1015,6 +1015,7 @@
     mode_t mask;
     int ret, initialData;
     bool isCanceled = false;
+    struct stat sstat = {};
 
     auto start = std::chrono::steady_clock::now();
 
@@ -1071,7 +1072,6 @@
             }
         }
     }
-    struct stat sstat;
     fstat(mfr.fd, &sstat);
     close(mfr.fd);