board: amlogic: odroid-n2: fix fdtfile suffix for n2-plus

board: amlogic: odroid-n2: fix fdtfile suffix for n2-plus

The N2+ dtb is meson-g12b-odroid-n2-plus.dtb, not n2_plus, so
correct the suffix provided in the board file. Also align the
board ident string shown during boot to match.

Fixes: 8bc780106c13 ("board: amlogic: odroid: add runtime detection of the N2/N2+/C4/HC4 variants")
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>