ASoC: dapm: mark dapm_kcontrol_get_wlist as global function

dapm_kcontrol_get_wlist() function needs to be called from
driver other than the soc-dapm.c file itself. Mark this
function as global function, so it can be accessed from
other drivers.

Change-Id: I87c1afc354c0f1700d6197e6993d0ecab7cf18f2
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>