linuxkpi: Include pr_err_once() in printk.h

[nc]

Summary

This is needed for the drm-kmod 5.7 import.

[• hselasky]

missing <tab> after #define .

And put the \ right after ...) like in the other macros.

Fix this and you're good to go.

[val_packett.cool]

Duplicate of D30672 ??