brcm63xx: HG655b: fix the imagetag at dts

brcm63xx: HG655b: fix the imagetag at dts

Fix the imagetag on the HG655b to allow a correct partition detection at boot time.

It turns out that it was defined at the wrong partition. Just move the imagetag to
the linux firmware partition.

The bug is present since the 18.06 release. Without this fix, the board won't boot.

Fixes: a27d59bb4274 ("brcm63xx: switch to new partition layout specification")
Signed-off-by: Daniel Gonzalez Cabanelas <dgcbueu@gmail.com>
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
(backported from 26d4cb2ca7acde1254f6ce6c0a54e0aca1489a0f)