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>

src/freedreno/registers/adreno/a5xx.xml

@@ -2882,7 +2882,7 @@ different border-color states per texture..  Looks something like:
 0340: 3c003c00 3c003c00 00000000 00000000 00000000 00000000 00000000 00000000
 
 		 -->
-		<bitfield name="BCOLOR_OFFSET" low="4" high="31"/>
+		<bitfield name="BCOLOR_OFFSET" low="7" high="31"/>
 	</reg32>
 	<reg32 offset="3" name="3"/>
 </domain>