crypto: ccp - Make function sev_get_firmware() static

Fixes the following sparse warning:

drivers/crypto/ccp/psp-dev.c:444:5: warning:
 symbol 'sev_get_firmware' was not declared. Should it be static?

Fixes: e93720606e ("crypto: ccp - Allow SEV firmware to be chosen based on Family and Model")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/ccp/psp-dev.c

@@ -441,7 +441,8 @@ static int sev_get_api_version(void)
 	return 0;
 }
 
-int sev_get_firmware(struct device *dev, const struct firmware **firmware)
+static int sev_get_firmware(struct device *dev,
+			    const struct firmware **firmware)
 {
 	char fw_name_specific[SEV_FW_NAME_SIZE];
 	char fw_name_subset[SEV_FW_NAME_SIZE];