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

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

The vdso64 portion of patch 74609f4536f2b8fd6a48381bbbe3cd37da20a527 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>