autoexposure: fix gain-min property definition
autoexposure: fix gain-min property definition

The "gain-min" property was setting its value to the "gain-max"
property. Furthermore the description was wrong.

Signed-off-by: Richard Leitner <0f2fdd4d2dfbb4dde6236fd550af0a2071b34781@skidata.com>

TheImagingSource/tiscamera,TheImagingSource/tiscamera,TheImagingSource/tiscamera,TheImagingSource/tiscamera