xen/libfdt: Fix comment following treewide __ASSEMBLY__ cleanup

This one comment didn't match the #ifdef symbol, and escaped conversion.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Michal Orzel <michal.orzel@amd.com>

xen/include/xen/libfdt/fdt.h

@@ -45,7 +45,7 @@ struct fdt_property {
 	char data[0];
 };
 
-#endif /* !__ASSEMBLY */
+#endif /* !__ASSEMBLER__ */
 
 #define FDT_MAGIC	0xd00dfeed	/* 4: version, 4: total size */
 #define FDT_TAGSIZE	sizeof(fdt32_t)