msm: camera: memmgr: Allow alloc flags with 0

Allocation flags need not be non-zero. In cases
where only allocation is required without mapping
the buffer to hw or kmd, flags can be 0.

Change-Id: Ia2b290ee0a3353ccac36f8aca569aa4edd48593f
Signed-off-by: Pavan Kumar Chilamkurthi <pchilamk@codeaurora.org>