safe_macros: Add SAFE_LSEEK().

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
readv01: Cleanup && make use of SAFE_MACROS().

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
readv01: Fix and simplify the testcase.

* There is no need to initialize buffers that
  are not used

* There is no need to prepare iovec vectors
  that are not used

* Fix the second readv() parameters
  (as reported by Helge Deller <deller@gmx.de>)

* Check that the buffer is read back correctly

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>