dma-buf/sw_sync: Fix kerneldoc warnings

drivers/dma-buf/sw_sync.c:248: warning: No description found for parameter 'obj'
drivers/dma-buf/sw_sync.c:248: warning: No description found for parameter 'value'
drivers/dma-buf/sw_sync.c:248: warning: Excess function parameter 'parent' description in 'sync_pt_create'
drivers/dma-buf/sw_sync.c:248: warning: Excess function parameter 'inc' description in 'sync_pt_create'

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180208113816.8288-1-chris@chris-wilson.co.uk