media: i2c: ov7251: Set VTS instead of having full tables for FPS.

The driver did have a full copy of the registers for each of
the 30, 60, and 90 fps modes. The main difference between them were
registers 0x380e/f which set the total height of the frame (VTS).

Remove the excess register settings, and Set that register value
explicitly for each mode.

This has dropped a change for the 30fps mode to registers 0x3016,
0x3017, 0x3018, 0x301a, 0x301b, and 0x301c. The data available
doesn't describe these registers, but the sensor seems fully
functional without the alternate settings.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>