crypto: cavium - Make cptvf_device_init static

Fix sparse warning:

drivers/crypto/cavium/cpt/cptvf_main.c:644:6:
 warning: symbol 'cptvf_device_init' was not declared. Should it be static?

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>