qlcnic: Fix NAPI poll routine for Tx completion

After d75b1ade ("net: less interrupt masking in NAPI")
driver's NAPI poll routine is expected to return
exact budget value if it wants to be re-called.

Signed-off-by: Shahed Shaikh <shahed.shaikh@qlogic.com>
Fixes: d75b1ade ("net: less interrupt masking in NAPI")
Signed-off-by: David S. Miller <davem@davemloft.net>