[jtag_riscv_agent] Fixed dout size in jtag_riscv_driver::send_csr_dr_req
[jtag_riscv_agent] Fixed dout size in jtag_riscv_driver::send_csr_dr_req

- dout field of jtag_riscv_driver::send_csr_dr_req was incorrectly
sized and as a result the top three bits of read data was being lost.

Signed-off-by: Nigel Scales <8a1721c0bc583c8de19e41073bf3ed3a1b00fc9d@gmail.com>

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