MAINTAINERS: Add #linux-pwm irc channel to pwm entry

The channel exists since quite a while, it's very low volume, so chances
are good that I see you starting a conversation.

Link: https://patch.msgid.link/20260309201954.1938136-2-ukleinek@kernel.org
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Author: Uwe Kleine-König

MAINTAINERS

@@ -21337,6 +21337,7 @@ M:	Uwe Kleine-König <ukleinek@kernel.org>
 L:	linux-pwm@vger.kernel.org
 S:	Maintained
 Q:	https://patchwork.ozlabs.org/project/linux-pwm/list/
+C:	irc://irc.libera.chat/linux-pwm
 T:	git https://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/linux.git
 F:	Documentation/devicetree/bindings/pwm/
 F:	Documentation/driver-api/pwm.rst