ALSA: pcxhr: "fix" PCXHR_REG_TO_PORT definition

The following preprocessor directive is non-compliant:

	#undef PCXHR_REG_TO_PORT(x)

gcc warns about extra tokens but nobody sees them as they are under if
branch which is never parsed.

Make it an #error, it is not clear to me what the author meant.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Link: https://lore.kernel.org/r/YUCCv47sm4zf9OVO@localhost.localdomain


Signed-off-by: Takashi Iwai <tiwai@suse.de>