msm: kgsl: fix stub declaration of kgsl_sync_timeline_create

This function needs to be 'static inline', not just 'static', to
avoid compiler warnings when CONFIG_SYNC is not defined.

Change-Id: Iaca9bc275d2fb8ccde2913137e81edb2d90a804e
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>