usb: gadget: configfs: make qw_sign attribute symmetric

Currently qw_sign requires UTF-8 character to set, but returns UTF-16
when read. This isn't obvious when simply using cat since the null
characters are not visible, but hexdump unveils the true string:

  # echo MSFT100 > os_desc/qw_sign
  # hexdump -C os_desc/qw_sign
  00000000  4d 00 53 00 46 00 54 00  31 00 30 00 30 00        |M.S.F.T.1.0.0.|

Make qw_sign symmetric by returning an UTF-8 string too. Also follow
common convention and add a new line at the end.
Reviewed-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/configfs.c

@@ -787,9 +787,13 @@ static ssize_t os_desc_b_vendor_code_store(struct config_item *item,
 static ssize_t os_desc_qw_sign_show(struct config_item *item, char *page)
 {
 	struct gadget_info *gi = os_desc_item_to_gadget_info(item);
+	int res;
 
-	memcpy(page, gi->qw_sign, OS_STRING_QW_SIGN_LEN);
-	return OS_STRING_QW_SIGN_LEN;
+	res = utf16s_to_utf8s((wchar_t *) gi->qw_sign, OS_STRING_QW_SIGN_LEN,
+			      UTF16_LITTLE_ENDIAN, page, PAGE_SIZE - 1);
+	page[res++] = '\n';
+
+	return res;
 }
 
 static ssize_t os_desc_qw_sign_store(struct config_item *item, const char *page,