cxl/uapi: Fix defined but not used warnings

Fix unused-const-variable warnings emitted by gcc when cxlmem.h is used
by pretty much all files except pci.c
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/163072205652.2250120.16833548560832424468.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

include/uapi/linux/cxl_mem.h

@@ -50,7 +50,7 @@ enum { CXL_CMDS };
 #define ___C(a, b) { b }
 static const struct {
 	const char *name;
-} cxl_command_names[] = { CXL_CMDS };
+} cxl_command_names[] __attribute__((__unused__)) = { CXL_CMDS };
 
 /*
  * Here's how this actually breaks out: