r6040: fix scheduling while atomic in r6040_tx_timeout

Add a helper function which only modifies R6040 MAC registers
use it when we timeout, and on adapter initialization. Fix
the scheduling while atomic but in the timeout routine due
to the reallocation of rx/tx buffers.

Signed-Off-By: Joerg Albert <jal2@gmx.de>
Signed-off-by: Florian Fainelli <florian.fainelli@telecomint.eu>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>