net: phy: meson-gxl: make function meson_gxl_read_status static

The function meson_gxl_read_status is local to the source and does
not need to be in global scope, so make it static.

Cleans up sparse warning:
symbol 'meson_gxl_read_status' was not declared. Should it be static?

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>