payloads: Fix typos

Change-Id: Ib7f1ba1766e5c972542ce7571a8aa3583c513823
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38911
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

payloads/libpayload/libc/readline.c

@@ -129,7 +129,7 @@ char *readline(const char *prompt)
 			if (ch < 0x20)
 				break;
 
-			/* ignore unprintables */
+			/* ignore unprintable characters */
 			if (ch >= 0x7f)
 				break;