all: Use stdplus::print over std::fprintf

Replacing `std::fprintf` with `stdplus::print`.
No logical change.

Tested: Buildable.
Signed-off-by: Michael Shen <gpgpgp@google.com>
Change-Id: I7050885c13e33244a4128aa519d163fd5b725098
diff --git a/ipmi.cpp b/ipmi.cpp
index 8e47c45..2c765be 100644
--- a/ipmi.cpp
+++ b/ipmi.cpp
@@ -34,6 +34,7 @@
 
 #include <ipmid/api-types.hpp>
 #include <ipmid/message.hpp>
+#include <stdplus/print.hpp>
 
 #include <cstdint>
 #include <cstdio>
@@ -87,7 +88,7 @@
         case SysLinuxBootDone:
             return linuxBootDone(data, handler);
         default:
-            std::fprintf(stderr, "Invalid subcommand: 0x%x\n", cmd);
+            stdplus::print(stderr, "Invalid subcommand: {:#x}\n", cmd);
             return ::ipmi::responseInvalidCommand();
     }
 }