r600g: take into account offset to system inputs at tgsi_interp_egcm()

r600g: take into account offset to system inputs at tgsi_interp_egcm()

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=100785
v2: I was too much twiddling whether to initialize nsys_inputs at the beginning of shader initialization or for allocation of system values, and by the time I decided to go with the first one, I forgot to change it back.

Signed-off-by: Constantine Kharlamov <Hi-Angel@yandex.ru>
Signed-off-by: Dave Airlie <airlied@redhat.com>