e_comp_wl_buffer: Refactoring for better code organization

e_comp_wl_buffer: Refactoring for better code organization

* Extracted common functionality into separate functions for readability
* Removed an unnecessary call to wl_buffer_send_release()[1]
* Made other minor changes for readability

[1]: Since `E_Comp_Wl_Buffer` has been created with ds_buffer, using
wl_buffer_send_release to send a release message is no longer necessary.
The backend implementation of ds_buffer will handle this automatically.

Change-Id: Ica32684c2a74be6d6e7aa1046ba446d8b1f29d56