Fix the return value of pack_pldm_header and unpack_pldm_header

- The intent behind this commit is to fix the return value of the
  pack_pldm_header and the unpack_pldm_header methods.

- According to PLDM spec, their return value should be `uint8_t`, not
  `int`, so 0 is PLDM_SUCCESS and non-0 is failure.

- Also, when we call the pack_pldm_header and unpack_pldm_header
  methods, we need to verify the return value of the method.

Tested: Built pldm successfully and Unit Test passes.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I0bd6838c4fb3b90f821c10324e4536ed352ffcfa
diff --git a/oem/ibm/libpldm/platform_oem_ibm.c b/oem/ibm/libpldm/platform_oem_ibm.c
index 1cf7e86..7090f95 100644
--- a/oem/ibm/libpldm/platform_oem_ibm.c
+++ b/oem/ibm/libpldm/platform_oem_ibm.c
@@ -9,14 +9,6 @@
 					   size_t payload_length,

 					   struct pldm_msg *msg)

 {

-	struct pldm_header_info header = {0};

-	int rc = PLDM_SUCCESS;

-

-	header.msg_type = PLDM_REQUEST;

-	header.instance = instance_id;

-	header.pldm_type = PLDM_PLATFORM;

-	header.command = PLDM_PLATFORM_EVENT_MESSAGE;

-

 	if (format_version != 1) {

 		return PLDM_ERROR_INVALID_DATA;

 	}

@@ -35,7 +27,13 @@
 		return PLDM_ERROR_INVALID_LENGTH;

 	}

 

-	if ((rc = pack_pldm_header(&header, &(msg->hdr))) > PLDM_SUCCESS) {

+	struct pldm_header_info header = {0};

+	header.msg_type = PLDM_REQUEST;

+	header.instance = instance_id;

+	header.pldm_type = PLDM_PLATFORM;

+	header.command = PLDM_PLATFORM_EVENT_MESSAGE;

+	uint8_t rc = pack_pldm_header(&header, &(msg->hdr));

+	if (rc != PLDM_SUCCESS) {

 		return rc;

 	}