UBI: rename _init_scan functions

We have a couple of initialization funcntionsn left which have "_scan" suffic -
rename them:

ubi_eba_init_scan() -> ubi_eba_init()
ubi_wl_init_scan() -> ubi_wl_init()

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>