MAINTAINERS: Add myself as a reviewer for RISC-V

As an active contributor to Xen's RISC-V port, so add myself
to the list of reviewers.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

MAINTAINERS

@@ -485,6 +485,7 @@ RISCV
 R:	Alistair Francis <alistair.francis@wdc.com>
 R:	Bob Eshleman <bobbyeshleman@gmail.com>
 R:	Connor Davis <connojdavis@gmail.com>
+R:	Oleksii Kurochko <oleksii.kurochko@gmail.com>
 S:	Supported
 F:	config/riscv64.mk
 F:	xen/arch/riscv/