MAINTAINERS: git://github.com -> https://github.com for sifive

Github deprecated the git:// links about a year ago, so let's move to
the https:// URLs instead.

Reported-by: Conor Dooley <[email protected]>
Link: https://github.blog/2021-09-01-improving-git-protocol-security-github/
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: palmer-dabbelt

MAINTAINERS

@@ -18777,7 +18777,7 @@ M:	Palmer Dabbelt <[email protected]>
 M:	Paul Walmsley <[email protected]>
 L:	[email protected]
 S:	Supported
-T:	git git://github.com/sifive/riscv-linux.git
+T:	git https://github.com/sifive/riscv-linux.git
 N:	sifive
 K:	[^@]sifive