msm: vidc: Fix the type of frame size

VIDIOC_ENUM_FRAMESIZES ioctl enumerate all frame sizes
that the device supports for the given pixel format. It
also provides the type of frame sizes the device supports.
The frame type supported is stepwise and it is continuous
i.e. the step size is 1. Keeping it as stepwise.

Change-Id: I9c801bd3dface3b1d1d824aea124e9c0666e09e1
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>