net: qca_spi: Avoid re-sync for single signature error

Setting a new network key would cause a reset of the QCA7000. Usually
the driver only notice the SPI interrupt and a single signature error.
So avoid the whole re-sync process (possible packet loss, transmit queue
stop and no carrier for at least 1 second) in this case.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: David S. Miller <davem@davemloft.net>