MAINTAINERS: add slimbus documentation

In the commit 202318d
slimbus documentation was added but it missed
the update in this file. Currently get_maintainer script
is missing the main maintainer.

Signed-off-by: anish kumar <yesanishhere@gmail.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20241230143354.266154-3-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: yesanishhere

MAINTAINERS

@@ -21242,6 +21242,7 @@ M:	Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
 L:	linux-sound@vger.kernel.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/slimbus/
+F:	Documentation/driver-api/slimbus.rst
 F:	drivers/slimbus/
 F:	include/linux/slimbus.h