riscv: Replace function-like macro by static inline function

The flush_icache_range() function is implemented as a "function-like
macro with unused parameters", which can result in "unused variables"
warnings.

Replace the macro with a static inline function, as advised by
Documentation/process/coding-style.rst.

Fixes: 08f051ed ("RISC-V: Flush I$ when making a dirty page executable")
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20250419111402.1660267-1-bjorn@kernel.org


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>