msm: vidc: Query the core on VIDIOC_G_FMT

Previously we only queried the core for buffer requirements in
VIDIOC_REQBUFS, and relied on that information in _G_FMT.  However,
there's no expectation that the client calls _REQBUFS before _G_FMT,
which leads to stale information being returned as part of _G_FMT.

As such, always retreive fresh info from the core for either ioctl.

Change-Id: Ife94343f4bd4f62da7f2bef4266076ceed409bca
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>