MAINTAINERS: Update SRP initiator entry

We have been asked to use our company e-mail address for open
source contributions. Hence this change from a personal e-mail
address into a company e-mail address.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>