drivers: video: ov5640: Some minor fixes and optimizations

Add some minor fixes and optimizations:

- Fix coding style
- Rename some variables
- Use the array variable size directly instead of defining a macro

Signed-off-by: Phi Bang Nguyen <phibang.nguyen@nxp.com>
Signed-off-by: Trung Hieu Le <trunghieu.le@nxp.com>