staging: et131x: Remove spinlock fbr_lock

The spinlock fbr_lock is only used in a single call sequence staring
from et131x_poll. As this call is already locked by napi->poll_lock,
we can remove it.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>