net/ibmvnic: Ignore H_FUNCTION return from H_EOI to tolerate XIVE mode

Reversion of commit 11d49ce9
(“net/ibmvnic: Fix EOI when running in XIVE mode.”) leaves us
calling H_EOI even in XIVE mode. That will fail with H_FUNCTION
because H_EOI is not supported in that mode. That failure is
harmless. Ignore it so we can use common code for both XICS and
XIVE.

Signed-off-by: Juliet Kim <julietk@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>