drivers/video: Fix -Wstringop-truncation in hdmi.c

Trying to copy into the string fields with strncpy() gives a warning from
gcc. Both fields are part of a packed HDMI header and do not require a
terminating \0 character.

../drivers/video/hdmi.c: In function 'hdmi_spd_infoframe_init':
../drivers/video/hdmi.c:230:2: warning: 'strncpy' specified bound 8 equals destination size [-Wstringop-truncation]
  230 |  strncpy(frame->vendor, vendor, sizeof(frame->vendor));
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../drivers/video/hdmi.c:231:2: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
  231 |  strncpy(frame->product, product, sizeof(frame->product));
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Just use memcpy() instead.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201021121241.17623-1-tzimmermann@suse.de

drivers/video/hdmi.c

@@ -221,14 +221,18 @@ EXPORT_SYMBOL(hdmi_avi_infoframe_pack);
 int hdmi_spd_infoframe_init(struct hdmi_spd_infoframe *frame,
 			    const char *vendor, const char *product)
 {
+	size_t len;
+
 	memset(frame, 0, sizeof(*frame));
 
 	frame->type = HDMI_INFOFRAME_TYPE_SPD;
 	frame->version = 1;
 	frame->length = HDMI_SPD_INFOFRAME_SIZE;
 
-	strncpy(frame->vendor, vendor, sizeof(frame->vendor));
-	strncpy(frame->product, product, sizeof(frame->product));
+	len = strlen(vendor);
+	memcpy(frame->vendor, vendor, min(len, sizeof(frame->vendor)));
+	len = strlen(product);
+	memcpy(frame->product, product, min(len, sizeof(frame->product)));
 
 	return 0;
 }