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>

.mailmap

@@ -70,6 +70,7 @@ Boris Brezillon <bbrezillon@kernel.org> <boris.brezillon@bootlin.com>
 Boris Brezillon <bbrezillon@kernel.org> <boris.brezillon@free-electrons.com>
 Brian Avery <b.avery@hp.com>
 Brian King <brking@us.ibm.com>
+Brian Silverman <bsilver16384@gmail.com> <brian.silverman@bluerivertech.com>
 Changbin Du <changbin.du@intel.com> <changbin.du@gmail.com>
 Changbin Du <changbin.du@intel.com> <changbin.du@intel.com>
 Chao Yu <chao@kernel.org> <chao2.yu@samsung.com>