watchdog: ziirave_wdt: Drop status polling code

Bootloader firmware doesn't implement DOWNLOAD_START or
DOWNLOAD_PACKET in a non-blocking way. It will stretch the clock of
the first status byte read until the operation is complete. Polling
for the status is not really necessary since it will always succed on
the first try. Replace polling code with a simple single byte read to
simplify things.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Rick Ramstetter <rick@anteaterllc.com>
Cc: linux-watchdog@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20190812200906.31344-20-andrew.smirnov@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>