conf: machines: Update barebox image for phyboard-segin-imx6ul-3
conf: machines: Update barebox image for phyboard-segin-imx6ul-3

The name of the barebox image for the low cost phyCORE-i.MX 6ULL changed
and needs to be adapted here.

Signed-off-by: Stefan Riedmueller <c3365f3fb46321e09058054bbbd3cb5c9c2c30f7@phytec.de>
Signed-off-by: Stefan Müller-Klieser <a3e08e35e4a42be768e7d0e76ae1ba321c2a66dd@phytec.de>

PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec