MAINTAINERS: add self as reviewer for AXI PWM GENERATOR

The initial author of the driver has moved on, so add the final
submitter (myself) as reviewer for the AXI PWM driver.

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20241017174744.902454-1-tgamblin@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Author: threexc

MAINTAINERS

@@ -3758,6 +3758,7 @@ F:	drivers/spi/spi-axi-spi-engine.c
 AXI PWM GENERATOR
 M:	Michael Hennerich <michael.hennerich@analog.com>
 M:	Nuno Sá <nuno.sa@analog.com>
+R:	Trevor Gamblin <tgamblin@baylibre.com>
 L:	linux-pwm@vger.kernel.org
 S:	Supported
 W:	https://ez.analog.com/linux-software-drivers