meta-efl: e-wm: renice to -2

A niceness of -10 is way too much, and it causes some audio problems
  such as buffer underruns/overruns with writei/readi with the
  fsoaudiod plugin responsible of sound during calls on the nokia900
  (and maybe other audio problems on other devices too).

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@no-log.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>