kdb: address -Wformat-security warnings

When -Wformat-security is not disabled, using a string pointer
as a format causes a warning:

kernel/debug/kdb/kdb_io.c: In function 'kdb_read':
kernel/debug/kdb/kdb_io.c:365:36: error: format not a string literal and no format arguments [-Werror=format-security]
  365 |                         kdb_printf(kdb_prompt_str);
      |                                    ^~~~~~~~~~~~~~
kernel/debug/kdb/kdb_io.c: In function 'kdb_getstr':
kernel/debug/kdb/kdb_io.c:456:20: error: format not a string literal and no format arguments [-Werror=format-security]
  456 |         kdb_printf(kdb_prompt_str);
      |                    ^~~~~~~~~~~~~~

Use an explcit "%s" format instead.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 5d5314d6 ("kdb: core for kgdb back end (1 of 2)")
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240528121154.3662553-1-arnd@kernel.orgSigned-off-by: Daniel Thompson <daniel.thompson@linaro.org>

kernel/debug/kdb/kdb_io.c

@@ -362,7 +362,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
 			if (i >= dtab_count)
 				kdb_printf("...");
 			kdb_printf("\n");
-			kdb_printf(kdb_prompt_str);
+			kdb_printf("%s",  kdb_prompt_str);
 			kdb_printf("%s", buffer);
 			if (cp != lastchar)
 				kdb_position_cursor(kdb_prompt_str, buffer, cp);
@@ -453,7 +453,7 @@ char *kdb_getstr(char *buffer, size_t bufsize, const char *prompt)
 {
 	if (prompt && kdb_prompt_str != prompt)
 		strscpy(kdb_prompt_str, prompt, CMD_BUFLEN);
-	kdb_printf(kdb_prompt_str);
+	kdb_printf("%s", kdb_prompt_str);
 	kdb_nextline = 1;	/* Prompt and input resets line number */
 	return kdb_read(buffer, bufsize);
 }