MAINTAINERS: SiFive drivers: change the git tree to a SiFive git tree

Update the git tree URL for drivers for SiFive-related IP blocks to
point to a SiFive-managed URL.

Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-riscv@lists.infradead.org
Signed-off-by: NPaul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: NPaul Walmsley <paul@pwsan.com>
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>

MAINTAINERS

@@ -13821,7 +13821,7 @@ F:	drivers/media/mmc/siano/
 SIFIVE DRIVERS
 M:	Palmer Dabbelt <palmer@sifive.com>
 L:	linux-riscv@lists.infradead.org
-T:	git git://git.kernel.org/pub/scm/linux/kernel/git/palmer/riscv-linux.git
+T:	git git://github.com/sifive/riscv-linux.git
 S:	Supported
 K:	sifive
 N:	sifive