contrib: gitdm: another IBM email

Based on Tom's LinkedIn profile his QEMU work was while in IBM's
virtualisation group.

Reviewed-by: Tom Musta <tommusta@gmail.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

contrib/gitdm/group-map-ibm

@@ -11,3 +11,4 @@ groug@kaod.org
 jcfaracco@gmail.com
 joel@jms.id.au
 sjitindarsingh@gmail.com
+tommusta@gmail.com