bcm2835_property: use cached values when querying framebuffer

bcm2835_property: use cached values when querying framebuffer

As the framebuffer settings are copied into the result message before it is
reconfigured, inconsistent behavior can happen when, for instance, you set with
a single message the width, height, and depth, and ask at the same time to
allocate the buffer and get the pitch and the size.

In this case, the reported pitch and size would be incorrect as they were
computed with the initial values of width, height and depth, not the ones the
client requested.

Signed-off-by: Sylvain Garrigues <[email protected]>
Reviewed-by: Andrew Baumann <[email protected]>
Message-id: 1461325343[email protected]
[PMM: folded a couple of long lines]
Signed-off-by: Peter Maydell <[email protected]>