audit: correct AUDIT_GET_FEATURE return message type

When an AUDIT_GET_FEATURE message is sent from userspace to the kernel, it
should reply with a message tagged as an AUDIT_GET_FEATURE type with a struct
audit_feature.  The current reply is a message tagged as an AUDIT_GET
type with a struct audit_feature.

This appears to have been a cut-and-paste-eo in commit b0fed402.

Reported-by: Steve Grubb <sgrubb@redhat.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>