net: airoha: move get_sport() callback at the beginning of airoha_enable_gdm2_loopback()

net: airoha: move get_sport() callback at the beginning of airoha_enable_gdm2_loopback()

Move the get_sport() callback invocation at the beginning of
airoha_enable_gdm2_loopback() routine in order to avoid leaving the
hardware in a partially configured state if get_sport() fails.
Previously, get_sport() was called after GDM2 forwarding, loopback,
channel, length, VIP and IFC registers had already been programmed.
A failure at that point would return an error leaving GDM2 with
loopback enabled but WAN port, PPE CPU port and flow control mappings
not configured.
Performing the get_sport() lookup before any register write guarantees
the routine either completes the full configuration sequence or exits
with no side effects on the hardware.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260608-airoha_enable_gdm2_loopback-minor-change-v1-1-1787a0f42b31@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>