libutil: Add stdio.h include in util_file.h

Without including stdio.h before util_file.h tye FILE type will not be
known leading to a build failure. Fix this by including stdio.h.

Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

include/lib/util_file.h

@@ -11,6 +11,8 @@
 #ifndef LIB_UTIL_FILE_H
 #define LIB_UTIL_FILE_H
 
+#include <stdio.h>
+
 #include "lib/util_exit_code.h"
 
 int util_file_read_line(char *str, size_t size, const char *fmt, ...);