MAINTAINERS: Cover RISC-V HTIF interface

The HTIF interface is RISC-V specific, add
it within the MAINTAINERS section covering
hw/riscv/.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20241129154304.34946-2-philmd@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

MAINTAINERS

@@ -324,8 +324,10 @@ S: Supported
 F: configs/targets/riscv*
 F: docs/system/target-riscv.rst
 F: target/riscv/
+F: hw/char/riscv_htif.c
 F: hw/riscv/
 F: hw/intc/riscv*
+F: include/hw/char/riscv_htif.h
 F: include/hw/riscv/
 F: linux-user/host/riscv32/
 F: linux-user/host/riscv64/