t_dd_dmatmp: Pull out common 'count -= count & 3' code
t_dd_dmatmp: Pull out common 'count -= count & 3' code

This was missing in the HAVE_TRIANGLES path, and that could cause
incorrect rendering.

No piglit regressions on i915 (G33) or radeon (Radeon 7500).

Signed-off-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38109
Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>
Cc: Marius Predut <506e8ef0f54c4b319fda4cea9c72fd8d10099c5d@intel.com>
Cc: "10.6 11.0" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler