riscv: Simplify base extension checks and direct boolean return

Reduce three lines checking to single line using a ternary conditional
expression for getting the base extension word. In addition, the
test_bit macro function already return a boolean which matches the
return type of the caller, so directly return the result of the test_bit
macro function.

Signed-off-by: Chin Yik Ming <yikming2222@gmail.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20250129203843.1136838-1-yikming2222@gmail.com


Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>