Fix "fastboot oem".

Broken by d6365a70527275f700b9594452020715a0c52510.

Bug: https://issuetracker.google.com/38216236
Test: "fastboot oem uart enable"
Change-Id: I672d5b96bb16fd77e7af61115b8a38606c691ea8
diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index f10b9ce..8a6877a 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -135,7 +135,7 @@
     return android::base::StringPrintf("%s/%s", dir, img_name);
 }
 
-std::string find_item(const std::string& item) {
+static std::string find_item(const std::string& item) {
     for (size_t i = 0; i < arraysize(images); ++i) {
         if (images[i].nickname && item == images[i].nickname) {
             return find_item_given_name(images[i].img_name);
@@ -1262,12 +1262,10 @@
 static void do_oem_command(std::vector<std::string>* args) {
     if (args->empty()) syntax_error("empty oem command");
 
-    std::string command;
+    std::string command("oem");
     while (!args->empty()) {
-        if (!command.empty()) command += ' ';
-        command += next_arg(args);
+        command += " " + next_arg(args);
     }
-
     fb_queue_command(command.c_str(), "");
 }