mailmap: Add entry for Rodrigo Siqueira

Map all of my previously used email addresses to my @igalia.com address.

Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Rodrigo Siqueira <siqueira@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>