drm/omap: gem: dumb: pitch is an output

drm/omap: gem: dumb: pitch is an output

When creating a dumb buffer object using the DRM_IOCTL_MODE_CREATE_DUMB
IOCTL, only the width, height, bpp and flags fields are inputs. The
caller is not guaranteed to zero out or set handle, pitch and size.
Drivers must not treat these values as possible inputs, otherwise they
may use uninitialized memory during the computation of the framebuffer
size.

The OMAP driver uses the pitch field passed in by userspace as a minimum
and only override it if the driver-computed pitch is larger than what
userspace provided. To prevent this from causing overallocation, fix the
minimum pitch to 0 to enforce the driver-computed pitch.

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Acked-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>