V4L/DVB: gspca - ov534: Fix and document setting manual exposure

Document that even if the state is a u8 value, both MSB and LSB are set
as sd->exposure represents half of the value we are going to set into
registers.

Skip setting exposure when AEC is enabled.
Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>
Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/gspca/ov534.c

@@ -686,6 +686,15 @@ static void setexposure(struct gspca_dev *gspca_dev)
 	struct sd *sd = (struct sd *) gspca_dev;
 	u8 val;
 
+	if (sd->aec)
+		return;
+
+	/* 'val' is one byte and represents half of the exposure value we are
+	 * going to set into registers, a two bytes value:
+	 * 
+	 *    MSB: ((u16) val << 1) >> 8   == val >> 7
+	 *    LSB: ((u16) val << 1) & 0xff == val << 1
+	 */
 	val = sd->exposure;
 	sccb_reg_write(gspca_dev, 0x08, val >> 7);
 	sccb_reg_write(gspca_dev, 0x10, val << 1);