phy: ti: gmii-sel: Fix register offset when parent is not a syscon node

phy: ti: gmii-sel: Fix register offset when parent is not a syscon node

When the node for this phy selector is a child node of a syscon node then the
property 'reg' is used as an offset into the parent regmap. When the node
is standalone and gets its own regmap this offset is pre-applied. So we need
to track which method was used to get the regmap and not apply the offset
in the standalone case.

Fixes: 1fdfa7cccd35 ("phy: ti: gmii-sel: Allow parent to not be syscon node")
Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Link: https://lore.kernel.org/r/20231025143302.1265633-1-afd@ti.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>