nvc0/ir: unset s/r indirect sources before moving everything

With the current logic, it's very likely that s/r indirect sources are
right after the "regular" ones. Unset them before moving the texture
arguments over rather than after, as one of those arguments would
likely have assumed one of the s/r positions.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
nvc0 retardo