wifi: wcn36xx: Slightly optimize PREPARE_HAL_BUF()

In most (likely all) cases, INIT_HAL_MSG() is called before
PREPARE_HAL_BUF().
In such cases calling memset() is useless because:
   msg_body.header.len = sizeof(msg_body)

So, instead of writing twice the memory, we just have a sanity check to
make sure that some potential trailing memory is zeroed.
It even gives the opportunity to see that by itself and optimize it away.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/7d8ab7fee45222cdbaf80c507525f2d3941587c1.1675371372.git.christophe.jaillet@wanadoo.fr

drivers/net/wireless/ath/wcn36xx/smd.c

@@ -475,8 +475,8 @@ static int wcn36xx_smd_send_and_wait(struct wcn36xx *wcn, size_t len)
 
 #define PREPARE_HAL_BUF(send_buf, msg_body) \
 	do {							\
-		memset(send_buf, 0, msg_body.header.len);	\
-		memcpy(send_buf, &msg_body, sizeof(msg_body));	\
+		memcpy_and_pad(send_buf, msg_body.header.len,	\
+			       &msg_body, sizeof(msg_body), 0);	\
 	} while (0)						\
 
 #define PREPARE_HAL_PTT_MSG_BUF(send_buf, p_msg_body) \