riscv: mm: add missing memcpy in kasan_init

Hi Atish,

It seems that the panic is due to the missing memcpy during kasan_init.
Could you please check whether this patch is helpful?

When doing kasan_populate, the new allocated base_pud/base_p4d should
contain kasan_early_shadow_{pud, p4d}'s content. Add the missing memcpy
to avoid page fault when read/write kasan shadow region.

Tested on:
 - qemu with sv57 and CONFIG_KASAN on.
 - qemu with sv48 and CONFIG_KASAN on.

Signed-off-by: Qinglin Pan <panqinglin2020@iscas.ac.cn>
Tested-by: Atish Patra <atishp@rivosinc.com>
Fixes: 8fbdccd2 ("riscv: mm: Support kasan for sv57")
Link: https://lore.kernel.org/r/20221009083050.3814850-1-panqinglin2020@iscas.ac.cn


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