usb: gadget: Remove snprintf() from sysfs call-backs and replace with sysfs_emit()

Since snprintf() has the documented, but still rather strange trait of
returning the length of the data that *would have been* written to the
array if space were available, rather than the arguably more useful
length of data *actually* written, it is usually considered wise to use
something else instead in order to avoid confusion.

In the case of sysfs call-backs, new wrappers exist that do just that.

This patch replaces just one use of snprintf() found in the sysfs
.show() call-back with the new sysfs_emit() helper.

Link: https://lwn.net/Articles/69419/
Link: https://github.com/KSPP/linux/issues/105
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20231130105459.3208986-5-lee@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/configfs.c

@@ -812,7 +812,7 @@ static ssize_t gadget_string_s_show(struct config_item *item, char *page)
 	struct gadget_string *string = to_gadget_string(item);
 	int ret;
 
-	ret = snprintf(page, sizeof(string->string), "%s\n", string->string);
+	ret = sysfs_emit(page, "%s\n", string->string);
 	return ret;
 }