MAINTAINERS: Update Atish's email address

I am no longer employed by western digital. Update my email address to
personal one and add entries to .mailmap as well.

Signed-off-by: Atish Patra <atishp@atishpatra.org>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
diff --git a/.mailmap b/.mailmap
index 6277bb2..29eedc1 100644
--- a/.mailmap
+++ b/.mailmap
@@ -50,6 +50,7 @@
 Ard Biesheuvel <ardb@kernel.org> <ard.biesheuvel@linaro.org>
 Arnaud Patard <arnaud.patard@rtp-net.org>
 Arnd Bergmann <arnd@arndb.de>
+Atish Patra <atishp@atishpatra.org> <atish.patra@wdc.com>
 Axel Dyks <xl@xlsigned.net>
 Axel Lin <axel.lin@gmail.com>
 Bart Van Assche <bvanassche@acm.org> <bart.vanassche@sandisk.com>