platform: Stabilise decode_pldm_platform_cper_event API

See usage example at:
[1] https://gerrit.openbmc.org/c/openbmc/pldm/+/63028/86/platform-mc/event_manager.cpp#77

Change-Id: I43c5c807f10ac38ee893e65a9d75fca76312d188
Signed-off-by: Thu Nguyen <thu@os.amperecomputing.com>
diff --git a/src/dsp/platform.c b/src/dsp/platform.c
index d7fc137..76b8992 100644
--- a/src/dsp/platform.c
+++ b/src/dsp/platform.c
@@ -3017,7 +3017,7 @@
 	return pldm_msgbuf_destroy_consumed(buf);
 }
 
-LIBPLDM_ABI_TESTING
+LIBPLDM_ABI_STABLE
 int decode_pldm_platform_cper_event(const void *event_data,
 				    size_t event_data_length,
 				    struct pldm_platform_cper_event *cper_event,
@@ -3072,7 +3072,7 @@
 	return pldm_msgbuf_destroy_consumed(buf);
 }
 
-LIBPLDM_ABI_TESTING
+LIBPLDM_ABI_STABLE
 uint8_t *
 pldm_platform_cper_event_event_data(struct pldm_platform_cper_event *event)
 {