crypto: hisilicon/zip - constify struct debugfs_reg32

hzip_dfx_regs is never changed and can be made const.

This allows the compiler to put it in the text section instead of the
data section.

Before:
   text    data     bss     dec     hex filename
  15236    6160     480   21876    5574 drivers/crypto/hisilicon/zip/zip_main.o

After:
   text    data     bss     dec     hex filename
  15620    5776     480   21876    5574 drivers/crypto/hisilicon/zip/zip_main.o

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Reviewed-by: Zhou Wang <wangzhou1@hisilicon.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>