qv4l2: general-tab: make sure m_width and height get a proper init value

qv4l2: general-tab: make sure m_width and height get a proper init value

m_width and m_height were not getting assigned any meaningful value on
startup, this causes the enum_frameintervals call inframeIntervalChanged
to fail. This patch makes sure that m_width and m_height get assigned
the actual width and height on startup, by setting them from updateVidCapFormat
this also removes the need for passing the actual width and height into
updateFrameSize and updateFrameInterval, they can now simply use
m_width and m_height since these are now always accurate.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>