regulator: Add UAPI headers to MAINTAINERS

The regulator UAPI headers were missing an entry in MAINTAINERS, add it.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://patch.msgid.link/20251222-maintainers-regulator-v1-1-7572390fdf1b@linutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: t-8ch

MAINTAINERS

@@ -27920,6 +27920,7 @@ F:	drivers/regulator/
 F:	rust/kernel/regulator.rs
 F:	include/dt-bindings/regulator/
 F:	include/linux/regulator/
+F:	include/uapi/regulator/
 K:	regulator_get_optional
 
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