Fix following sparse warnings:

drivers/crypto/cavium/zip/zip_crypto.c:72:5: warning: symbol 'zip_ctx_init' was not declared. Should it be static?
drivers/crypto/cavium/zip/zip_crypto.c:110:6: warning: symbol 'zip_ctx_exit' was not declared. Should it be static?
drivers/crypto/cavium/zip/zip_crypto.c:122:5: warning: symbol 'zip_compress' was not declared. Should it be static?
drivers/crypto/cavium/zip/zip_crypto.c:158:5: warning: symbol 'zip_decompress' was not declared. Should it be static?
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>