add std namespace prefix to common methods

Standard clib methods should be explicitly grabbed from the standard
namespace.

Change-Id: I8bcfcb260a99180d535ec8102c1a24c318cbc209
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/ipmi_fru_info_area.cpp b/ipmi_fru_info_area.cpp
index 47979e9..949d546 100644
--- a/ipmi_fru_info_area.cpp
+++ b/ipmi_fru_info_area.cpp
@@ -5,6 +5,7 @@
 #include <map>
 #include <numeric>
 #include <phosphor-logging/elog.hpp>
+
 namespace ipmi
 {
 namespace fru
@@ -184,8 +185,8 @@
             std::copy(fru_raw, fru_raw + 3, std::back_inserter(data));
             return;
         }
-        fprintf(stderr, "MgfDate invalid date: %u secs since UNIX epoch\n",
-                static_cast<unsigned int>(raw));
+        std::fprintf(stderr, "MgfDate invalid date: %u secs since UNIX epoch\n",
+                     static_cast<unsigned int>(raw));
     }
     // Blank date
     data.emplace_back(0);