I2S doxygen example to match mcux examples, clarify SPI Receive

[juhakivekas]

Prerequisites

• I have checked latest main branch and the issue still exists.
• I did not see it is stated as known-issue in release notes.
• No similar GitHub issue is related to this change.
• My code follows the commit guidelines of this project.
• I have performed a self-review of my own code.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.

Tiny documentation fixes, no code changes

The doxygen examples were incorrect so I made them look the way they are in the codes from mcux-sdk-examples. Clarified that SPI receive also send the transfer