i830: Fix stack corruption

i830: Fix stack corruption

Found by compiler warning:
    i830_texstate.c:131:28: warning: argument to 'sizeof' in 'memset' call
          is the same expression as the destination; did you mean to
          dereference it?  [-Wsizeof-pointer-memaccess]
       memset(state, 0, sizeof(state));
              ~~~~~            ^~~~~

On 64-bit systems, memset here would write an extra 4 bytes.

Note: This is a candidate for the stable branches.
Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>