sfc: remove EFX_BUG_ON_PARANOID, use EFX_WARN_ON_[ONCE_]PARANOID instead

Logically, EFX_BUG_ON_PARANOID can never be correct.  For, BUG_ON should
 only be used if it is not possible to continue without potential harm;
 and since the non-DEBUG driver will continue regardless (as the BUG_ON is
 compiled out), clearly the BUG_ON cannot be needed in the DEBUG driver.
So, replace every EFX_BUG_ON_PARANOID with either an EFX_WARN_ON_PARANOID
 or the newly defined EFX_WARN_ON_ONCE_PARANOID.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>