2976 remove useless offsetof() macros

@@ -72,10 +72,11 @@
 #include <sys/dkio.h>
 #include <sys/vtoc.h>
 #include <sys/cmn_err.h>
 #include <sys/modctl.h>
 #include <sys/ddi.h>
+#include <sys/sysmacros.h>
 #include <sys/sunddi.h>
 #include <sys/sunldi.h>
 #include <sys/nsctl/nsvers.h>
 
 #include <sys/nsc_thread.h>

@@ -2413,15 +2414,10 @@
         }
 
         return (0);
 }
 
-
-#ifndef offsetof
-#define offsetof(s, m)  ((size_t)(&((s *)0)->m))
-#endif
-
 /*
  * re-write the size of the current partition
  */
 static int
 sv_fix_dkiocgvtoc(const intptr_t arg, const int mode, sv_dev_t *svp)