nv50/ir: fix srcMask computation for TG4 and TXF
This affects which inputs are marked as used. In a situation where only the texture instruction uses an input, it might have been ignored as unused due to input masks. Affects subtests of KHR-GL45.texture_cube_map_array.sampling Signed-off-by:Ilia Mirkin <imirkin@alum.mit.edu> Cc: mesa-stable@lists.freedesktop.org (cherry picked from commit 054c54d1)