drm/armada: Fix off-by-one error in armada_overlay_get_property()

[ Upstream commit 5f0d984053f74983a287100a9519b2fabb785fb5 ]

As ffs() returns one more than the index of the first bit set (zero
means no bits set), the color key mode value is shifted one position too
much.

Fix this by using FIELD_GET() instead.

Fixes: c96103b6 ("drm/armada: move colorkey properties into overlay plane state")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/a4d779d954a7515ddbbf31cb0f0d8184c0e7c879.1689600265.git.geert+renesas@glider.be


Signed-off-by: Sasha Levin <sashal@kernel.org>