iris: consider bufmgr creation to have failed if `dup`ing of the fd fails

iris: consider bufmgr creation to have failed if `dup`ing of the fd fails

Coverity points out that we can pass a negative value to `close()`,
which results in an unchecked error. While this is technically true, it
really isn't a problem as `close()` is speced to return -1 in that case
(which we ignore). However, what is true is that if we fail to dup the
fd (the only case where we could end up with a negative value), then
we're in an unrecoverable error state anyway, and should go to the error
cleanup code.

CID: 1521539
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Marcin Ślusarz <marcin.slusarz@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21568>