Fix VDSO gettimeofday() when called with NULL struct timeval.

The vdso64 portion of patch 74609f45 for
fixing problems with NULL gettimeofday input mistakenly checks for a
null tz field twice, when it should be checking for null tz once, and
null tv once; by way of a r10/r11 typo.

Any application calling gettimeofday(&tv,NULL) will "fail".

This corrects that typo, and makes my G5 happy.

Tested on G5.

Signed-off-by: Will Schmidt <will_schmidt@vnet.ibm.com>
Cc: Tony Breeds <tony@bakeyournoodle.com>
Forwarded-by: Ben Herrenschmidt <benh@kernel.crashing.org>

[ Ben says: "I checked the 32 bits part of the change is correct.  You
  can probably blame me for originally writing the 2 versions with
  inversed usage of r10 and r11, thus confusing Tony :-)"

  Ben duly blamed.   - Linus ]

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>