staging: fsl-mc: dpmng: drop unused prototype

The implementation was removed in commit:

decd3d0c (staging: fsl-mc: uprev binary interface to match MC v10.x)

but the prototype was left behind.

Also fix a message that was wrongly mentioning it.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Acked-by: Stuart Yoder <stuart.yoder@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>