security/capabilities: remove check for -EINVAL

bprm_caps_from_vfs_caps() never returned -EINVAL so remove the
rc == -EINVAL check.

Signed-off-by: Christian Brauner <christian@brauner.io>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: James Morris <james.morris@microsoft.com>