media: dvb-usb: pctv452e: move snd/rcv len check before kmalloc

syzbot reported a uninit-value in pctv452e_i2c_msg. [1]

When the snd_len or rcv_len check fails and jumps to failed, buf is
uninitialized, triggering the uninit-value issue.

Move the snd/rcv length check before kmalloc, and return -EINVAL directly
if the condition is met.

[1]
BUG: KMSAN: uninit-value in hex_string+0x681/0x740 lib/vsprintf.c:1220
pctv452e_i2c_msg+0x82a/0x8f0 drivers/media/usb/dvb-usb/pctv452e.c:467
pctv452e_i2c_xfer+0x2e6/0x4c0 drivers/media/usb/dvb-usb/pctv452e.c:502

Reported-by: [e-mail]
Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
Signed-off-by: Edward Adam Davis <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/usb/dvb-usb/pctv452e.c

···
 	u8 id;
 	int ret;
 
+	if (snd_len > 64 - 7 || rcv_len > 64 - 7)
+		return -EINVAL;
+
 	buf = kmalloc(64, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
 	id = state->c++;
-
-	ret = -EINVAL;
-	if (snd_len > 64 - 7 || rcv_len > 64 - 7)
-		goto failed;
 
 	buf[0] = SYNC_BYTE_OUT;
 	buf[1] = id;