mmc: atmel-mci: fix data timeout issue

The data timeout timer was configured after mmc_add_host call. So, with bad
timings, it was possible to have a mmc request causing mod_timer call on a
non setup timer.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>