speakup: Fix sizeof() vs ARRAY_SIZE() bug

The "buf" pointer is an array of u16 values.  This code should be
using ARRAY_SIZE() (which is 256) instead of sizeof() (which is 512),
otherwise it can the still got out of bounds.

Fixes: c8d2f34e ("speakup: Avoid crash on very long word")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/d16f67d2-fd0a-4d45-adac-75ddd11001aa@moroto.mountainSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/accessibility/speakup/main.c

@@ -574,7 +574,7 @@ static u_long get_word(struct vc_data *vc)
 	}
 	attr_ch = get_char(vc, (u_short *)tmp_pos, &spk_attr);
 	buf[cnt++] = attr_ch;
-	while (tmpx < vc->vc_cols - 1 && cnt < sizeof(buf) - 1) {
+	while (tmpx < vc->vc_cols - 1 && cnt < ARRAY_SIZE(buf) - 1) {
 		tmp_pos += 2;
 		tmpx++;
 		ch = get_char(vc, (u_short *)tmp_pos, &temp);