net/bnxt: fix Rx timestamp when FIFO pending bit is set

net/bnxt: fix Rx timestamp when FIFO pending bit is set

Fix to clear the Rx FIFO while reading the timestamp.
If the Rx FIFO has pending bit set, keep reading to clear it
and return the last valid timestamp instead of unconditionally
returning an error.

Fixes: b11cceb83a34 ("net/bnxt: support timesync")
Cc: stable@dpdk.org
Signed-off-by: Somnath Kotur <somnath.kotur@broadcom.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>