freedreno/a5xx: Fix up border color pointers.

freedreno/a5xx: Fix up border color pointers.

We were forgetting to increment in the loop, but also it looks from blob
dumps on Pixel 2 like all the pointers it emitted were shifted up by 3
compared to our xml, and that's the same shift that a6xx uses for its
pointers.  None of the tests seem to use more than one
border-color-requiring texture, so it's hard to tell.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9904>