Fix for 58dc8b7: dest regions must not use HorzStride 0 in ExecSize 1

Fix for 58dc8b7: dest regions must not use HorzStride 0 in ExecSize 1

Quoting section 11.3.10, paragraph 10.2 of the 965PRM:

10.2. 	If ExecSize is 1, dst.HorzStride must not be 0. Note that this is
	relaxed from rule 10.1.2. Also note that this rule for destination
	horizontal stride is different from that for source as stated in
	rule #7.

GM45 gets very angry when rule 10.2 is violated.

Patch 58dc8b7 (i965: support destination horiz strides in align1 access mode)
added support for additional horizontal strides in the ExecSize 1 case, but
failed to notice that mesa occasionally re-purposes a register as a
temporary destination, even though it was constructed as a repeating source
with HorzStride = 0.

While, ideally, we should probably fix the code using these register
specifications, this patch simply rewrites them to use HorzStride 1 as the
pre-58dc8b7 code did.

Signed-off-by: Keith Packard <keithp@keithp.com>