media: atomisp: fix uninitialized stack mem usage in ia_css_rmgr_acq_vbuf()

When ia_css_rmgr_acq_vbuf() enters the code path where it uses the local
"struct ia_css_rmgr_vbuf_handle v" on the stack it relies on v.count==0
so that ia_css_rmgr_refcount_retain_vbuf allocates a new handle.

Explicitly set v.count to 0 rather then it being whatever was on the stack.

Link: https://lore.kernel.org/linux-media/20220612160556.108264-3-hdegoede@redhat.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>