mailmap: fix Ricardo's entry

Commit df48b234 (".mailmap: Add all the mail alias for Ricardo
Ribalda") assigned two different proper names for the email address
"ricardo.ribalda@uam.es".  This is a completely wrong usage as the
mailmap feature exists for coalescing together commits by the same
person whose name is sometimes spelled differently.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>