r600: don't use shader key without verifying shader type (v2)

r600: don't use shader key without verifying shader type (v2)

Since 7a32652231f96eac14c4bfce02afe77b4132fb77
r600: Turn 'r600_shader_key' struct into union

we were accessing key fields that might be aliased in the union
with other fields, so we should check what shader type we are
compiling for before using key values from it.

v1.1: make it compile
v2: have caffeine, make it work - we don't set type
until later, so don't reference it until we've set it.

Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Cc: "11.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>