hw/riscv/virt.c: fix aclint soc/mtimer nodename

Running 'dtc' to generate a readable fdt for the virt machine produce
warnings:

 $ dtc -I dtb -O dts virt.dtb > virt.dts
<stdout>: Warning (simple_bus_reg): /soc/mtimer@2000000: simple-bus unit address format error, expected "2007ff8"
<stdout>: Warning (simple_bus_reg): /soc/mtimer@2008000: simple-bus unit address format error, expected "200fff8"

This happens because the 'reg' field does not match the address in the
nodename.  The right fix, pointed out by Chao in [1], is to make the
nodename match the reg value:

"In the current QEMU implement, `addr` is the MTIMECMP base address,
while the MTIME register is located at addr + RISCV_ACLINT_DEFAULT_MTIME."

In other words, the 'reg' value is correct but the nodename isn't.

We'll make the fix now, allowing the next patch to move the fixed version
of aclint FDT to fdt-common.

[1] https://lore.kernel.org/qemu-devel/apHH1upnh8udUUT-@ChaodeMacBook-Pro.local/

Cc: qemu-stable@nongnu.org
Suggested-by: Chao Liu <chao.liu@processmission.com>
Fixes: 954886ea6d ("hw/riscv: virt: Add optional ACLINT support to virt machine")
Signed-off-by: Daniel Henrique Barboza <daniel.barboza@oss.qualcomm.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Chao Liu <chao.liu@processmission.com>
Message-ID: <20260828203918.350131-9-daniel.barboza@oss.qualcomm.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
(cherry picked from commit 9d6ac47d3182f2bdadea4bed596c82759a167e67)
(Mjt: drop format string change (it was corrected in subsequent change),
  but keep the value change)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>