board: bananapi-m1: Fix to use dtb instead of dts
boot.cmd using dts file instead of dtb which was
added in below commit, so fix the same.
"board: Add Bananapi M1 support"
(sha1: 5f50fb8d1df51b622537da015f8c3b7b6dcbbc35)
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>