media: gspca: Add error handling for stv06xx_read_sensor()

In hdcs_init(), the return value of stv06xx_read_sensor() needs to be
checked. A proper implementation can be found in vv6410_dump(). Add a
check in loop condition and propergate error code to fix this issue.

Fixes: 4c98834a ("V4L/DVB (10048): gspca - stv06xx: New subdriver.")
Cc: stable@vger.kernel.org # v2.6+
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>