misc: atsha204a: fix wakeup function

misc: atsha204a: fix wakeup function

The ATSHA204A chip requires SDA line to go low for at least 60us to
wake up the chip. Previous implementation did not meet this requirement
due to the NAK received on bus and not sending the zeroes.
The function to ignore the NAK and send bytes regardless is not
supported in the u-boot making it impossible to wake up the chip
this way.
Instead, the bus speed, if needed, is set to lowest value and the
message is sent to the address 0x0. This way, the address of zero
makes the SDA line go low for about 80us, meeting the required time
to wake up the chip. The zero length packet is not sent by the i2c,
so the one byte is sent to the transfer function, but only the address
is sent anyway.
After sending the zero address, the bus speed is restored to the
previous value if it was slowed down to wake up the chip.

Signed-off-by: Michał Barnaś <barnas@google.com>