media: ov9650: add a sanity check

As pointed by cppcheck:

[drivers/media/i2c/ov9650.c:706]: (error) Shifting by a negative value is undefined behaviour
[drivers/media/i2c/ov9650.c:707]: (error) Shifting by a negative value is undefined behaviour
[drivers/media/i2c/ov9650.c:721]: (error) Shifting by a negative value is undefined behaviour

Prevent mangling with gains with invalid values.

As pointed by Sylvester, this should never happen in practice,
as min value of V4L2_CID_GAIN control is 16 (gain is always >= 16
and m is always >= 0), but it is too hard for a static analyzer
to get this, as the logic with validates control min/max is
elsewhere inside V4L2 core.

Reviewed-by: Sylwester Nawrocki <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/i2c/ov9650.c

···
 		for (m = 6; m >= 0; m--)
 			if (gain >= (1 << m) * 16)
 				break;
+
+		/* Sanity check: don't adjust the gain with a negative value */
+		if (m < 0)
+			return -EINVAL;
+
 		rgain = (gain - ((1 << m) * 16)) / (1 << m);
 		rgain |= (((1 << m) - 1) << 4);