octeontx2-af: Add additional register check to rvu_poll_reg()

Check one more time before exiting the API with an error.
Fix API to poll at least twice, in case there are other high priority
tasks and this API doesn't get CPU cycles for multiple jiffies update.

In addition, increase timeout from usecs_to_jiffies(10000) to
usecs_to_jiffies(20000), to prevent the case that for CONFIG_100HZ
timeout will be a single jiffies.
A single jiffies results actual timeout that can be any time between
1usec and 10msec. To solve this, a value of usecs_to_jiffies(20000)
ensures that timeout is 2 jiffies.

Signed-off-by: Smadar Fuks <smadarf@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>