net: stmmac: Fix mixed enum type warning

The commit 5a558611 ("net: stmmac: support FPE link partner
hand-shaking procedure") introduced the following coverity warning:

  "Parse warning (PW.MIXED_ENUM_TYPE)"
  "1. mixed_enum_type: enumerated type mixed with another type"

This is due to both "lo_state" and "lp_sate" which their datatype are
enum stmmac_fpe_state type, and being assigned with "FPE_EVENT_UNKNOWN"
which is a macro-defined of 0. Fixed this by assigned both these
variables with the correct enum value.

Fixes: 5a558611

 ("net: stmmac: support FPE link partner hand-shaking procedure")
Signed-off-by: Wong Vee Khee <vee.khee.wong@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>