Revert "fix return check for KVM_GET_DIRTY_LOG ioctl"

This reverts commit b533f658a98325d0e47b36113bd9f5bcc046fdae.

The original code was wrong, because effectively it ignored errors
from kernel, because kernel does not return -1 on error case but
returns -errno, and does not return -EPERM for this particular ioctl.
But in some cases kernel actually returned unsuccessful result,
namely, when the dirty bitmap in requested slot does not exist
it returns -ENOENT.  With new code this condition becomes an
error when it shouldn't be.

Revert that patch instead of fixing it properly this late in the
release process.  I disagree with this approach, but let's make
things move _somewhere_, instead of arguing endlessly whch of
the 2 proposed fixes is better.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Message-id: 1397477644-902-1-git-send-email-mjt@msgid.tls.msk.ru
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>