linux-user/riscv: Fix handling of cpu mask in riscv_hwprobe syscall

linux-user/riscv: Fix handling of cpu mask in riscv_hwprobe syscall

The third argument of the syscall contains the size of the
cpu mask in bytes, not bits.  Nor is the size rounded up to
a multiple of sizeof(abi_ulong).

Cc: qemu-stable@nongnu.org
Reported-by: Andreas Schwab <schwab@suse.de>
Fixes: 9e1c7d982d7 ("linux-user/riscv: Add syscall riscv_hwprobe")
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250308225902.1208237-3-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
(cherry picked from commit 1a010d22b7adecf0fb1c069e1e535af1aa51e9cf)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>