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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Takashi Iwai <[e-mail]>

sound/pci/pcxhr/pcxhr_core.c

···
 #define PCXHR_DSP 2
 
 #if (PCXHR_DSP_OFFSET_MAX > PCXHR_PLX_OFFSET_MIN)
-#undef  PCXHR_REG_TO_PORT(x)
+#error  PCXHR_REG_TO_PORT(x)
 #else
 #define PCXHR_REG_TO_PORT(x)	((x)>PCXHR_DSP_OFFSET_MAX ? PCXHR_PLX : PCXHR_DSP)
 #endif