fix MINIO_KMS_SECRET_KEY env. variable parsing (#12200)

This commit fixes a bug when parsing the env. variable
`MINIO_KMS_SECRET_KEY`. Before, the env. variable
name - instead of its value - was parsed. This (obviously)
did not work properly.

This commit fixes this.

Signed-off-by: Andreas Auernhammer <aead@mail.de>

cmd/common-main.go

@@ -340,7 +340,7 @@ func handleCommonEnvVars() {
 	}
 
 	if env.IsSet(config.EnvKMSSecretKey) {
-		GlobalKMS, err = kms.Parse(config.EnvKMSSecretKey)
+		GlobalKMS, err = kms.Parse(env.Get(config.EnvKMSSecretKey, ""))
 		if err != nil {
 			logger.Fatal(err, "Unable to parse the KMS secret key inherited from the shell environment")
 		}