zfs: Use a statement expression to implement SET_ERROR()

This way we can avoid making assumptions about the SDT probe
implementation.  No functional change intended.

This was submitted upstream as openzfs/zfs#16284

sys/contrib/openzfs/include/os/freebsd/spl/sys/sdt.h

@@ -31,13 +31,14 @@
 
 #include_next <sys/sdt.h>
 #ifdef KDTRACE_HOOKS
-/* CSTYLED */
+/* BEGIN CSTYLED */
 SDT_PROBE_DECLARE(sdt, , , set__error);
 
-#define	SET_ERROR(err) \
-	((sdt_sdt___set__error->id ? \
-	(*sdt_probe_func)(sdt_sdt___set__error->id, \
-	    (uintptr_t)err, 0, 0, 0, 0) : 0), err)
+#define	SET_ERROR(err)	({					\
+	SDT_PROBE1(sdt, , , set__error, (uintptr_t)err);	\
+	err;							\
+})
+/* END CSTYLED */
 #else
 #define	SET_ERROR(err) (err)
 #endif