target/riscv: use riscv_csrr in riscv_csr_read

target/riscv: use riscv_csrr in riscv_csr_read

Commit 38c83e8d3a33 ("target/riscv: raise an exception when CSRRS/CSRRC
writes a read-only CSR") changed the behavior of riscv_csrrw, which
would formerly be treated as read-only if the write mask were set to 0.

Fixes an exception being raised when accessing read-only vector CSRs
like vtype.

Fixes: 38c83e8d3a33 ("target/riscv: raise an exception when CSRRS/CSRRC writes a read-only CSR")
Signed-off-by: stove <stove@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20250827203617.79947-1-stove@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>