Address CR feedback round #2-2

Fix casing

Author: saad-ali

csi.proto

@@ -150,7 +150,7 @@ message CreateVolumeRequest {
   // End user credentials used to authenticate/authorize volume creation
   // request.
   // This field is OPTIONAL.
-  Credentials userCredentials = 6;
+  Credentials user_credentials = 6;
 }
 
 message CreateVolumeResponse {
@@ -282,7 +282,7 @@ message Credentials {
   // This information is sensitive and MUST be treated as such (not logged,
   // etc.) by the CO.
   // This field is REQUIRED.
-  map<string, string> Data = 1;
+  map<string, string> data = 1;
 }
 ////////
 ////////
@@ -333,7 +333,7 @@ message ControllerPublishVolumeRequest {
   // End user credentials used to authenticate/authorize controller publish
   // request.
   // This field is OPTIONAL.
-  Credentials userCredentials = 6;
+  Credentials user_credentials = 6;
 }
 
 message ControllerPublishVolumeResponse {
@@ -577,7 +577,7 @@ message NodePublishVolumeRequest {
 
   // End user credentials used to authenticate/authorize node publish request.
   // This field is OPTIONAL.
-  Credentials userCredentials = 8;
+  Credentials user_credentials = 8;
 }
 
 message NodePublishVolumeResponse {