msm: camera: memmgr: update correct length in bufq

In a corner case, race condition to free the original
ion buf allocated and new ion buffer with same fd but
different size after freeing the origianl ion buf might
result into mismatches in the real ion buf size assigned
in bufq. To avoid this update length in bufq with
local variable.

CRs-Fixed: 3142221
Change-Id: I8241544dba7609662d01f8d765e8d171b8288baa
Signed-off-by: Tejas Prajapati <quic_tpraja@quicinc.com>