net: fddi: skfp: ecm: Protect 'if' when AIX_EVENT is not defined

net: fddi: skfp: ecm: Protect 'if' when AIX_EVENT is not defined

When AIX_EVENT is not defined, the 'if' body will be empty, which
makes GCC complain.  Place bracketing around the invocation to protect
it.

Fixes the following W=1 kernel build warning(s):

 drivers/net/fddi/skfp/ecm.c: In function ‘ecm_fsm’:
 drivers/net/fddi/skfp/ecm.c:153:29: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body]

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201102114512.1062724-2-lee.jones@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>