pldm_types.h: add #ifndef wrapper

Make this a once-only header.

Change-Id: Ib6cd915de8d97a1ba25fb632c45299c7593068ca
Signed-off-by: Jinu Joy Thomas <jthomas7@in.ibm.com>
diff --git a/libpldm/pldm_types.h b/libpldm/pldm_types.h
index 32228d7..7ff1527 100644
--- a/libpldm/pldm_types.h
+++ b/libpldm/pldm_types.h
@@ -1,3 +1,6 @@
+#ifndef PLDM_TYPES_H
+#define PLDM_TYPES_H
+
 #include <stdint.h>
 
 typedef union {
@@ -23,3 +26,5 @@
 	uint8_t update;
 	uint8_t alpha;
 } __attribute__((packed)) ver32_t;
+
+#endif /* PLDM_TYPES_H */