.mailmap: add Christophe Ricard

Different computers had different settings in the mail client.  Some
contributions appear as Christophe Ricard, others as Christophe RICARD.

Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>