hw/riscv/virt.c: change imsic nodename to 'interrupt-controller'

hw/riscv/virt.c: change imsic nodename to 'interrupt-controller'

The Linux DT docs for imsic [1] predicts an 'interrupt-controller@addr'
node, not 'imsic@addr', given this node inherits the
'interrupt-controller' node.

[1] Documentation/devicetree/bindings/interrupt-controller/riscv,imsics.yaml

Reported-by: Conor Dooley <conor@kernel.org>
Fixes: 28d8c281200f ("hw/riscv: virt: Add optional AIA IMSIC support to virt machine")
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20240531202759.911601-7-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>