dma-buf: Fix a typo in Kconfig

A 'h' ismissing in' syncronization'

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200216114708.20583-1-christophe.jaillet@wanadoo.fr