drm/ssd130x: Drop _helper prefix from struct drm_*_helper_funcs callbacks

The driver uses a naming convention where functions for struct drm_*_funcs
callbacks are named ssd130x_$object_$operation, while the callbacks for
struct drm_*_helper_funcs are named ssd130x_$object_helper_$operation.

The idea is that this helper_ prefix in the function names denote that are
for struct drm_*_helper_funcs callbacks. This convention was copied from
other drivers when ssd130x was written, but Maxime pointed out that is the
exception rather than the norm.

So let's get rid of the _helper prefixes from the function handlers names.

Suggested-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230914195138.1518065-1-javierm@redhat.com