RISC-V: Use a less ugly workaround for unused variable warnings

Thanks to Christoph Hellwig for pointing out a cleaner way to do this,
as my approach was quite ugly.

CC: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/sys_riscv.c

@@ -65,24 +65,11 @@ SYSCALL_DEFINE6(mmap2, unsigned long, addr, unsigned long, len,
 SYSCALL_DEFINE3(riscv_flush_icache, uintptr_t, start, uintptr_t, end,
 	uintptr_t, flags)
 {
-#ifdef CONFIG_SMP
-	struct mm_struct *mm = current->mm;
-	bool local = (flags & SYS_RISCV_FLUSH_ICACHE_LOCAL) != 0;
-#endif
-
 	/* Check the reserved flags. */
 	if (unlikely(flags & ~SYS_RISCV_FLUSH_ICACHE_ALL))
 		return -EINVAL;
 
-	/*
-	 * Without CONFIG_SMP flush_icache_mm is a just a flush_icache_all(),
-	 * which generates unused variable warnings all over this function.
-	 */
-#ifdef CONFIG_SMP
-	flush_icache_mm(mm, local);
-#else
-	flush_icache_all();
-#endif
+	flush_icache_mm(current->mm, flags & SYS_RISCV_FLUSH_ICACHE_LOCAL);
 
 	return 0;
 }