e1000e: Avoid hw_error if legacy mode used

https://bugzilla.redhat.com/show_bug.cgi?id=1787142


The emulation issues hw_error if PSRCTL register
is written, for example, with zero value.
Such configuration does not present any problem when
DTYP bits of RCTL register define legacy format of
transfer descriptors. Current commit discards check
for BSIZE0 and BSIZE1 when legacy mode used.

Acked-by: Dmitry Fleytman <dmitry.fleytman@gmail.com>
Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>