RISC-V: Kconfig: Remove trailing whitespace

Remove trailing whitespace that hurts my eyes.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/080aa959266ad842a8e7efca7111f1350c6a065a.1673424858.git.geert+renesas@glider.beSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>