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

sound/pci/pcxhr/pcxhr_core.c

@@ -52,7 +52,7 @@
 #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