MAINTAINERS: update ClangBuiltLinux IRC chat

Everyone has moved from Freenode to Libera so updated the channel entry
for MAINTAINERS.

Link: ClangBuiltLinux#1402
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: nathanchance

MAINTAINERS

@@ -4498,7 +4498,7 @@ L:	[email protected]
 S:	Supported
 W:	https://clangbuiltlinux.github.io/
 B:	https://github.com/ClangBuiltLinux/linux/issues
-C:	irc://chat.freenode.net/clangbuiltlinux
+C:	irc://irc.libera.chat/clangbuiltlinux
 F:	Documentation/kbuild/llvm.rst
 F:	include/linux/compiler-clang.h
 F:	scripts/clang-tools/