net: airoha: Fix wrong GDM4 register definition

net: airoha: Fix wrong GDM4 register definition

Fix wrong GDM4 register definition, in Airoha SDK GDM4 is defined at
offset 0x2400 but this doesn't make sense as it does conflict with the
CDM4 that is in the same location.

Following the pattern where each GDM base is at the FWD_CFG, currently
GDM4 base offset is set to 0x2500. This is correct but REG_GDM4_FWD_CFG
and REG_GDM4_SRC_PORT_SET are still using the SDK reference with the
0x2400 offset. Fix these 2 define by subtracting 0x100 to each register
to reflect the real address location.

Fixes: 23020f049327 ("net: airoha: Introduce ethernet support for EN7581 SoC")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20250120154148.13424-1-ansuelsmth@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>