omap_dumb: improve error reporting in omap_bo_del
omap_dumb: improve error reporting in omap_bo_del

Hopefully we will never see any of these messages.
However, just in case, let's log what happened just before we assert().

Also assert() if munmap fails.

Signed-off-by: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>

BUG=chromium:272670
TEST=sanity check UI
TEST=start ui;  sleep 10; stop ui
   check for any new error messages during omap_bo_del in:
    /var/log/Xorg.0.log

Change-Id: I63c8bb1b725c36007fc64a90666074d7aecb49d9
Reviewed-on: https://chromium-review.googlesource.com/190690
Reviewed-by: John Sheu <e133b36fa071c0f7efb4cebd35fa1371d3ae789d@chromium.org>
Reviewed-by: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>
Commit-Queue: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>
Tested-by: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>

markyzq/armsoc-rockchip,markyzq/armsoc-rockchip