net: ethernet: ti: am65-cpts: update ret when ptp_clock is ERROR

We always have to update the value of ret, otherwise the
 error value may be the previous one.

Fixes: f6bd5952 ("net: ethernet: ti: introduce am654 common platform time sync driver")
Signed-off-by: Wang Qing <wangqing@vivo.com>
[grygorii.strashko@ti.com: fix build warn, subj add fixes tag]
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Link: https://lore.kernel.org/r/20201112164541.3223-1-grygorii.strashko@ti.com


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