fb: cfb_shell: use shell_strtol in cmd_set_kerning

Switch from using direct `strtol` calls to `shell_strtol`.
This change leverages the extensive error handling provided
by `shell_strtol`.

Signed-off-by: Pisit Sawangvonganan <[email protected]>

Author: ndrs-pst

subsys/fb/cfb_shell.c

@@ -340,18 +340,16 @@ static int cmd_set_font(const struct shell *sh, size_t argc, char *argv[])
 
 static int cmd_set_kerning(const struct shell *sh, size_t argc, char *argv[])
 {
-	int err;
-	char *ep = NULL;
+	int err = 0;
 	long kerning;
 
 	if (!dev) {
 		shell_error(sh, HELP_INIT);
 		return -ENODEV;
 	}
 
-	errno = 0;
-	kerning = strtol(argv[1], &ep, 10);
-	if (errno || ep == argv[1]) {
+	kerning = shell_strtol(argv[1], 10, &err);
+	if (err) {
 		shell_error(sh, HELP_INIT);
 		return -EINVAL;
 	}