staging/speakup: fix checkpatch.pl warning in speak_char()

correct the following warning from checkpatch.pl:-

WARNING: Prefer using '"%s...", __func__' to using 'speak_char', this
function's name, in a string
Signed-off-by: Justin Skists <j.skists@gmail.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/main.c

@@ -447,7 +447,7 @@ static void speak_char(u16 ch)
 
 	cp = spk_characters[ch];
 	if (!cp) {
-		pr_info("speak_char: cp == NULL!\n");
+		pr_info("%s: cp == NULL!\n", __func__);
 		return;
 	}
 	if (IS_CHAR(ch, B_CAP)) {