Drop one from the two dent's mode variables used in shim_dentry

[rainfld]

In the shim layer, two variables are used for keeping track of the mode, one is shim_dentry::mode and the other is shim_file_data:mode while a pointer to an instance of shim_file_data is kept in shim_dentry.

These two variables are updated and used in different places and sometimes are out of sync. For future, we should use one copy for the mode value and keep the other one as a reference.

[donporter]

Agreed. I think shim_file_data is probably the one we want.