riscv: Fix wrong size passed to local_flush_tlb_range_asid()

local_flush_tlb_range_asid() takes the size as argument, not the end of
the range to flush, so fix this by computing the size from the end and
the start of the range.

Fixes: 7a92fc8b ("mm: Introduce flush_cache_vmap_early()")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>