Add const specifiers to posix and nuttx I2C class constructors and transfer() methods

[mcsauder]

Describe problem solved by the proposed pull request
This PR adds const specifiers to the posix and nuttx I2C class constructors and transfer() method arguments. Currently, a few of the arguments have const specifiers and this work adds const to the remaining arguments.

Test data / coverage
This PR was test flown on a 250 quad with pixhawk 4 mini. (The pixhawk mini primary mag, the IST8310, is I2C.)

Flight tests perform the same as current PX4:master branch

• https://review.px4.io/plot_app?log=e26208b0-a13a-4f88-8004-273bd996a6d6

Please let me know if you have any questions on this PR! Thanks!

-Mark

[dagar]

The receive buffer shouldn't be const.

[mcsauder]

The receive buffer shouldn't be const.

Yes. Agreed. But we can expect the pointer to the buffer to not change during the execution of the method, though, right?

[dagar]

Declare a pointer to a const uint8_t type.

const uint8_t * buf

Declare a const pointer to a uint8_t type.

const * uint8_t buf

Both.

const * uint8_t * buf

[mcsauder]

Thanks for pointing that out @dagar, I've removed the const specifiers from the receive buffers added in the previous commit, specifying them the right (intended) way is just really ugly.

I'm still curious how that worked at all:

Let me know if you'd like to see anything else done with this PR! Thanks!

[TSC21]

@mcsauder can you rebase?

[mcsauder]

Rebased and commits squashed. Thanks for the ping @TSC21 !

[mcsauder]

Closing, merged with PR #12695.