MAINTAINERS: Add entry for generic-radix-tree

lib/generic-radix-tree.c is a simple radix tree that supports storing
arbitrary types. Add a maintainers entry for it.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

MAINTAINERS

@@ -8739,6 +8739,13 @@ S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/linux-pm.git
 F:	drivers/genpd/
 
+GENERIC RADIX TREE
+M:	Kent Overstreet <kent.overstreet@linux.dev>
+S:	Supported
+C:	irc://irc.oftc.net/bcache
+F:	include/linux/generic-radix-tree.h
+F:	lib/generic-radix-tree.c
+
 GENERIC RESISTIVE TOUCHSCREEN ADC DRIVER
 M:	Eugen Hristev <eugen.hristev@microchip.com>
 L:	linux-input@vger.kernel.org