sfc: Use correct macro to set event bitfield

falcon_sim_phy_event() used EFX_OWORD_FIELD, which operates on
bitfields in 128-bit values, on an event, which is a 64-bit value.
This should be harmless - these macros always use little-endian
ordering, so it would read and write back the following 8 bytes
unchanged - but it is obviously wrong.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>