sunrpc: avoid -Wformat-security warning

Using a non-constant string as an sprintf-style is potentially dangerous:

net/sunrpc/svc.c: In function 'param_get_pool_mode':
net/sunrpc/svc.c:164:32: error: format not a string literal and no format arguments [-Werror=format-security]

Use a literal "%s" format instead.

Fixes: 5f71f3c32553 ("sunrpc: refactor pool_mode setting code")
Signed-off-by: Arnd Bergmann <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>

net/sunrpc/svc.c

···
 	str[len] = '\n';
 	str[len + 1] = '\0';
 
-	return sysfs_emit(buf, str);
+	return sysfs_emit(buf, "%s", str);
 }
 
 module_param_call(pool_mode, param_set_pool_mode, param_get_pool_mode,