drm/i915: Fix slightly botched merge in __reloc_entry_gpu

This function should be an int, not a bool.

Presumably because we had the same 2 reverts in a slightly different
way, git got confused.

Thanks to Dan for reporting. :)

The conflict is between the 3 reverts in drm-fixes:

4993a8a3 ("Revert "drm/i915: Remove i915_gem_object_get_dirty_page()"")
ad5d95e4 ("Revert "drm/i915/gem: Async GPU relocations only"")
20561da3 ("Revert "drm/i915/gem: Delete unused code"")

And the slightly different combined revert in drm-intel-gt-next, but
with the same goal:

102a0a90 ("Revert "drm/i915/gem: Async GPU relocations only"")

In the merge commit 1f4b2aca ("Merge tag
'drm-intel-gt-next-2020-09-07' of git://anongit.freedesktop.org/drm/drm-intel

 into drm-next") things
went wrong, but the merge commit view now doesn't show any conflict
anymore (as git tends to do when the resolution picks one or the other
branch).

The need to handle other than just true/false error codes in
__reloc_entry_gpu was added in the dma_resv locking changes in
c43ce123 ("drm/i915: Use per object locking in execbuf, v12.")

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Dave Airlie <airlied@redhat.com>
[danvet: Explain this entire saga a lot better, adding tons of commit
references. Also note that this was merged before full intel-gfx-CI
results, only after BAT, since the breakage at the BAT run is already
severe enough to block all pre-merge testing.]
Fixes: 1f4b2aca ("Merge tag 'drm-intel-gt-next-2020-09-07' of git://anongit.freedesktop.org/drm/drm-intel

 into drm-next")
Acked-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200910111225.2184193-1-maarten.lankhorst@linux.intel.com