media: ext-ctrls-flash.rst: fix typo

to synchronises -> to synchronise

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/uapi/v4l/ext-ctrls-flash.rst

@@ -98,7 +98,7 @@ Flash Control IDs
 	V4L2_CID_FLASH_STROBE control.
     * - ``V4L2_FLASH_STROBE_SOURCE_EXTERNAL``
       - The flash strobe is triggered by an external source. Typically
-	this is a sensor, which makes it possible to synchronises the
+	this is a sensor, which makes it possible to synchronise the
 	flash strobe start to exposure start.