at86rf230: change reset timings

While checkpatch another patch I got a:

"WARNING: msleep < 20ms can sleep for up to 20ms"

The datasheet of at86rf231 and at86rf212 says a minimum delay for reset
pulse width and spi access latency after reset is 625 nanoseconds.

This patch removes the 1 milliseconds sleep and replace it with a 1
microseconds udelay which should be also okay for the reset pulse width.

To change the state from RESET -> TRX_OFF the at86rf230 device needs 120
microseconds, this is a worst case of all at86rf* chips.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>