vcl: Fix the ldp init check

vcl: Fix the ldp init check

Maybe some function calls the wrapper funtion like read which invokes
the ldp_init_check in the other libs as a constructor before
ldp_constructor. Then the ldp has been initialized already when
ldp_constructor is invoked. And it's normal case, we shouldn't treat it
as an error.

So ldp_init should return success if ldp is initialized already instead
of an assert.

Type: fix

Change-Id: Ifa2a7b1d5471981a3f840b14a4fa5d48fb1f1374
Signed-off-by: Gao Feng <gfree.wind@outlook.com>