staging: rtl8723bs: core: Change return type of init_mlme_ext_priv

As init_mlme_ext_priv function always returns SUCCESS , We can change
return type from int to void.

Fixes below issue identified by coccicheck
drivers/staging/rtl8723bs/core/rtw_mlme_ext.c:464:5-8: Unneeded
variable: "res". Return "_SUCCESS" on line 492

Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
Link: https://lore.kernel.org/r/20190715174618.GA8947@hari-Inspiron-1545


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>