mailmap: update email address of Brian Silverman

Brian Silverman's address at bluerivertech.com is not valid anymore,
use Brian's private email address instead.

Link: https://lore.kernel.org/all/20220110082359.2019735-1-mkl@pengutronix.de


Cc: Brian Silverman <bsilver16384@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>