riscv: mm: Fixup compat arch_get_mmap_end

riscv: mm: Fixup compat arch_get_mmap_end

When the task is in COMPAT mode, the arch_get_mmap_end should be 2GB,
not TASK_SIZE_64. The TASK_SIZE has contained is_compat_mode()
detection, so change the definition of STACK_TOP_MAX to TASK_SIZE
directly.

Cc: stable@vger.kernel.org
Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Leonardo Bras <leobras@redhat.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20231222115703.2404036-3-guoren@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>