crypto: stm32 - Save 54 CSR registers

The CSR registers go from 0 to 53.  So the number of registers
should be 54.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>