msm: ispif: fix a bug in checking the validity of vfe intf

Parse the whole length of vfe intf to the validate function to avoid
the situation that the lower 8bits pass the validation while intf is
crafted to a large value which can cause buffer overflow later.

CRs-Fixed: 2008469
Change-Id: I0de19ec36d73918ab2f38eb7ba1f833c02a3face
Signed-off-by: Junzhe Zou <jnzhezou@codeaurora.org>