MAINTAINERS: add an IRC entry for RISC-V

I remember being told "Just ping me on IRC" about patches, but googling
at the time was not helpful. #riscv on libera is not linux specific,
but a bunch of contributors etc do hang out there.
Add a link to the maintainers entry to help others find it in the future!

Signed-off-by: Conor Dooley <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: ConchuOD

MAINTAINERS

@@ -17948,6 +17948,7 @@ M:	Albert Ou <[email protected]>
 L:	[email protected]
 S:	Supported
 Q:	https://patchwork.kernel.org/project/linux-riscv/list/
+C:	irc://irc.libera.chat/riscv
 P:	Documentation/riscv/patch-acceptance.rst
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git
 F:	arch/riscv/