ravb: Remove manual pause frame transmit

Writing a non-zero value to the manual PAUSE frame register (MPR) starts
the transmission of a PAUSE frame.
A PAUSE frame is sent in ravb_emac_init(), but it is not expected behavior.

Signed-off-by: Masaru Nagai <masaru.nagai.vx@renesas.com>
Signed-off-by: Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Acked-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>