docs: fix, intel_guc_loader.c has been moved to intel_guc_fw.c

docs: fix, intel_guc_loader.c has been moved to intel_guc_fw.c

With commit d9e2e0143c the 'GuC-specific firmware loader' doc
section was removed from intel_guc_loader.c without a
replacement.  So lets remove it from the Kernel-doc::

  .. kernel-doc:: drivers/gpu/drm/i915/intel_guc_loader.c
     :doc: GuC-specific firmware loader

With commit e8668bbcb0 intel_guc_loader.c was renamed to to
intel_guc_fw.c and to name just one, intel_guc_init_hw() was
renamed to intel_guc_fw_upload(). Since we get errors in the
Sphinx build like:

- Error: Cannot open file ./drivers/gpu/drm/i915/intel_guc_loader.c

Change the kernel-doc directive from intel_guc_loader.c to
intel_guc_fw.c

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
[danvet: Rebase onto the partial fix 006c23327f8d
("documentation/gpu/i915: fix docs build error after file rename")]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1513078717-12373-1-git-send-email-markus.heiser@darmarit.de