media: em28xx: adjust I2C timeout according with I2C speed

If the I2C speed is too slow, it should wait more for an
answer.

While here, change disconnected type from char to unsigned
int, just like all other bitmask fields there at em28xx
struct.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>