drm/i915: Stub out i915_gpu_coredump_put

i915_gpu_coreddump_put is currently only defined if
CONFIG_DRM_I915_CAPTURE_ERROR is enabled, provide a stub otherwise.

Reported-by: Mike Lothian <mike@fireburn.co.uk>
Fixes: 742379c0 ("drm/i915: Start chopping up the GPU error capture")
Fixes: 74831738 ("drm/i915/execlists: Offline error capture")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mike Lothian <mike@fireburn.co.uk>
Cc: Andi Shyti <andi.shyti@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200124192255.541355-1-chris@chris-wilson.co.uk