i915: Fix value returned for PIPE_CAP_MAX_TEXTURE_CUBE_LEVELS
Found by inspection while reviewing !27561 (closed). Original code was returning the size instead of the number of levels. This was probably an over zealous search-and-replace when PIPE_CAP_MAX_TEXTURE_2D_LEVELS
was renamed PIPE_CAP_MAX_TEXTURE_2D_SIZE
.
Fixes: 0c31fe9e ("gallium: Redefine the max texture 2d cap from _LEVELS to _SIZE.")