libpldm: correct GET_SENSOR_READING_REQ_BYTES to 3 bytes

As section 18.2 GetSensorReading command in PLDM specification
DSP0248, the payload size of request data of GetSensorReading command
is 3 bytes. This commit corrects GET_SENSOR_READING_REQ_BYTES to match
with the spec.

Resolves openbmc/pldm#31.

Signed-off-by: ThuBaNguyen <thu@os.amperecomputing.com>
Change-Id: I15979423c8ff629d32469a087ea2a140f029ce91
diff --git a/libpldm/platform.h b/libpldm/platform.h
index 962bad0..8c95a27 100644
--- a/libpldm/platform.h
+++ b/libpldm/platform.h
@@ -15,7 +15,7 @@
 #define PLDM_SET_STATE_EFFECTER_STATES_REQ_BYTES 19
 #define PLDM_GET_STATE_SENSOR_READINGS_REQ_BYTES 4
 #define PLDM_GET_NUMERIC_EFFECTER_VALUE_REQ_BYTES 2
-#define PLDM_GET_SENSOR_READING_REQ_BYTES 4
+#define PLDM_GET_SENSOR_READING_REQ_BYTES 3
 #define PLDM_SET_EVENT_RECEIVER_REQ_BYTES 5
 /* Response lengths are inclusive of completion code */
 #define PLDM_SET_STATE_EFFECTER_STATES_RESP_BYTES 1