crypto: ccree - constify struct debugfs_reg32

pid_cd_regs and debug_regs are never changed and can therefore 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
   2871    2320      64    5255    1487 drivers/crypto/ccree/cc_debugfs.o

After:
   text    data     bss     dec     hex filename
   3255    1936      64    5255    1487 drivers/crypto/ccree/cc_debugfs.o

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