hw/riscv: sifive_gpio: Clean up the codes

hw/riscv: sifive_gpio: Clean up the codes

Do various minor clean-ups to the exisiting codes for:

- coding convention conformance
- remove unnecessary blank lines
- spell SiFive correctly

Signed-off-by: Bin Meng <[email protected]>
Reviewed-by: Alistair Francis <[email protected]>
Message-id: 1591625864[email protected]
Message-Id: <1591625864[email protected]>
Signed-off-by: Alistair Francis <[email protected]>