drm/i915: Make WAIT_IOCTL negative timeouts be indefinite again

drm/i915: Make WAIT_IOCTL negative timeouts be indefinite again

This fixes a regression from

commit 5ed0bdf21a85d78e04f89f15ccf227562177cbd9
Author: Thomas Gleixner <[email protected]>
Date:   Wed Jul 16 21:05:06 2014 +0000

    drm: i915: Use nsec based interfaces

that made a negative timeout return immediately rather than the
previously defined behaviour of waiting indefinitely.

Testcase: igt/gem_wait
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89494
Signed-off-by: Chris Wilson <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Ben Widawsky <[email protected]>
Cc: Kristian Høgsberg <[email protected]>
Cc: [email protected]
Reviewed-by: Daniel Vetter <[email protected]>
[Jani: fixed a checkpatch complaint about whitespace.]
Signed-off-by: Jani Nikula <[email protected]>