drm/i915/guc: Do not use 0 for GuC doorbell cookie

drm/i915/guc: Do not use 0 for GuC doorbell cookie

Apparently, this value is reserved and may be interpreted as changing
doorbell ownership. Even though we're not observing any side effects
now, let's skip over it to be consistent with the spec.

v2: Apply checkpatch (Sagar)

Suggested-by: Sagar Arun Kamble <[email protected]>
Signed-off-by: Michał Winiarski <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Sagar Arun Kamble <[email protected]>
Reviewed-by: Sagar Arun Kamble <[email protected]>
Signed-off-by: Chris Wilson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]