crypto: mxs-dcp - make symbols 'sha1_null_hash' and 'sha256_null_hash' static

Fixes the following sparse warnings:

drivers/crypto/mxs-dcp.c:39:15: warning:
 symbol 'sha1_null_hash' was not declared. Should it be static?
drivers/crypto/mxs-dcp.c:43:15: warning:
 symbol 'sha256_null_hash' was not declared. Should it be static?

Fixes: c709eeba ("crypto: mxs-dcp - Fix SHA null hashes and output length")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/mxs-dcp.c

@@ -36,11 +36,11 @@
  * Null hashes to align with hw behavior on imx6sl and ull
  * these are flipped for consistency with hw output
  */
-const uint8_t sha1_null_hash[] =
+static const uint8_t sha1_null_hash[] =
 	"\x09\x07\xd8\xaf\x90\x18\x60\x95\xef\xbf"
 	"\x55\x32\x0d\x4b\x6b\x5e\xee\xa3\x39\xda";
 
-const uint8_t sha256_null_hash[] =
+static const uint8_t sha256_null_hash[] =
 	"\x55\xb8\x52\x78\x1b\x99\x95\xa4"
 	"\x4c\x93\x9b\x64\xe4\x41\xae\x27"
 	"\x24\xb9\x6f\x99\xc8\xf4\xfb\x9a"