media: hi556: correct the test pattern configuration

Hynix hi556 support 8 test pattern modes:
hi556_test_pattern_menu[] = {
{
	"Disabled",
	"Solid Colour",
	"100% Colour Bars",
	"Fade To Grey Colour Bars",
	"PN9",
	"Gradient Horizontal",
	"Gradient Vertical",
	"Check Board",
	"Slant Pattern",
}

The test pattern is set by a 8-bit register according to the
specification.
+--------+-------------------------------+
| BIT[0] |  Solid color                  |
+--------+-------------------------------+
| BIT[1] |  Color bar                    |
+--------+-------------------------------+
| BIT[2] |  Fade to grey color bar       |
+--------+-------------------------------+
| BIT[3] |  PN9                          |
+--------+-------------------------------+
| BIT[4] |  Gradient horizontal          |
+--------+-------------------------------+
| BIT[5] |  Gradient vertical            |
+--------+-------------------------------+
| BIT[6] |  Check board                  |
+--------+-------------------------------+
| BIT[7] |  Slant pattern                |
+--------+-------------------------------+
Based on function above, current test pattern programming is wrong.
This patch fixes it by 'BIT(pattern - 1)'. If pattern is 0, driver
will disable the test pattern generation and set the pattern to 0.

Fixes: e6213840 ("media: hi556: Add support for Hi-556 sensor")
Cc: stable@vger.kernel.org
Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>