Fix the prefix matching for uncrypt status.

Also change its logging statement from PLOG to LOG, since
android::base::StartsWith() doesn't set errno.

Test: Build and reboot into recovery image. Check last_log.

Change-Id: I55ac7eec24228db76a13580958b4a4330b06cf57
diff --git a/install.cpp b/install.cpp
index 427bea1..72c922d 100644
--- a/install.cpp
+++ b/install.cpp
@@ -377,8 +377,8 @@
         std::string uncrypt_status;
         if (!android::base::ReadFileToString(UNCRYPT_STATUS, &uncrypt_status)) {
             PLOG(WARNING) << "failed to read uncrypt status";
-        } else if (!android::base::StartsWith(uncrypt_status, "uncrypt_:")) {
-            PLOG(WARNING) << "corrupted uncrypt_status: " << uncrypt_status;
+        } else if (!android::base::StartsWith(uncrypt_status, "uncrypt_")) {
+            LOG(WARNING) << "corrupted uncrypt_status: " << uncrypt_status;
         } else {
             log_buffer.push_back(android::base::Trim(uncrypt_status));
         }