i965/vec4: Initialize LOD to 0.0f for textureQueryLevels() and texture().

i965/vec4: Initialize LOD to 0.0f for textureQueryLevels() and texture().

We implement textureQueryLevels (which takes no arguments, save the
sampler) using the resinfo message (which takes an argument of LOD).
Without initializing it, we'd generate a MOV from the null register to
load the LOD argument.

Essentially the same logic applies to texture. A vertex shader cannot
compute derivatives and so cannot produce an LOD, so TXL with an LOD of
0.0 is used.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>