media: imx258: Limit the max analogue gain to 480

The range for analog gain mentioned in the datasheet is [0, 480].
The real gain formula mentioned in the datasheet is:

	Gain = 512 / (512 – X)

Hence, values larger than 511 clearly makes no sense. The gain
register field is also documented to be of 9-bits in the datasheet.

Certainly, it is enough to infer that, the kernel driver currently
advertises an arbitrary analog gain max. Fix it by rectifying the
value as per the data sheet i.e. 480.

Signed-off-by: Umang Jain <[email protected]>
Reviewed-by: Laurent Pinchart <[email protected]>
Reviewed-by: Dave Stevenson <[email protected]>
Signed-off-by: Sakari Ailus <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>

drivers/media/i2c/imx258.c

@@ -47,7 +47,7 @@
 /* Analog gain control */
 #define IMX258_REG_ANALOG_GAIN		0x0204
 #define IMX258_ANA_GAIN_MIN		0
-#define IMX258_ANA_GAIN_MAX		0x1fff
+#define IMX258_ANA_GAIN_MAX		480
 #define IMX258_ANA_GAIN_STEP		1
 #define IMX258_ANA_GAIN_DEFAULT		0x0