net: ethernet: renesas: Fix return type in rswitch_etha_wait_link_verification()

The rswitch_etha_wait_link_verification() is supposed to return zero
on success or negative error codes.  Unfortunately it is declared as a
bool so the caller treats everything as success.

Fixes: 3590918b

 ("net: ethernet: renesas: Add support for "Ethernet Switch"")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/Y3OPo6AOL6PTvXFU@kili
Signed-off-by: Paolo Abeni <pabeni@redhat.com>