smb: client: Fix a NULL vs IS_ERR() check in wsl_set_xattrs()

This was intended to be an IS_ERR() check.  The ea_create_context()
function doesn't return NULL.

Fixes: 1eab17fe485c ("smb: client: add support for WSL reparse points")
Reviewed-by: Paulo Alcantara <pc@manguebit.com>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Steve French <stfrench@microsoft.com>