net: thunder_bgx: decrement cleanup index before use

All paths in probe that call goto defer do so before assigning phydev
and thus it makes sense to cleanup the prior index. It also fixes a bug
where index 0 does not get cleaned up.

Fixes: b7d3e3d3 ("net: thunderx: Don't leak phy device references on -EPROBE_DEFER condition.")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250901213314.48599-1-rosenp@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>