ax88796c: fix fetching error stats from percpu containers

rx_dropped, tx_dropped, rx_frame_errors and rx_crc_errors are being
wrongly fetched from the target container rather than source percpu
ones.
No idea if that goes from the vendor driver or was brainoed during
the refactoring, but fix it either way.

Fixes: a97c69ba

 ("net: ax88796c: ASIX AX88796C SPI Ethernet Adapter Driver")
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Acked-by: Łukasz Stelmach <l.stelmach@samsung.com>
Link: https://lore.kernel.org/r/20211023121148.113466-1-alobakin@pm.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>