Remove superfluous check from null_ptr_check

[niederha]

The null_ptr_check() function checks that dev.inft_ptr is not NULL, however, nowhere in the code it this pointer used.
Indeed dev.inf_ptr is only used in user defined functions: read, write and delay_us... hence if it is up to the user to use the pointer it should be up to the user to check it.

In the current state of things if the user doesn't want to use the pointer he would still have to assign it a value in order to pass the init, which is, imo, a bad practice.

Thus removing the check makes sense.

[niederha]

@boschsensortec Any update? I know this is but a detail, but it would help me clean some code to get this mr passer. And if it doesn't work for semantic reasons, I'd be curious to know why