soc/samsung/exynos5420: Refactor fimd vidtcon access

soc/samsung/exynos5420: Refactor fimd vidtcon access

Accessing the higher vidtcon variables using pointer arithmetic from the
lower address FIMD_CTRL struct is undefined behaviour, since pointers
manipulations are not allowed outside the objects they point to. The
standard-blessed way is to perform the arithmetic using integer
addresses first, and then convert that to a pointer. The end result is
the same, but avoids the risk of unsafe optimizations from an
over-zealous compiler.

Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Found-by: Coverity CID 1402096, 1402124, 1402131, 1402169
Change-Id: I13ed23836e8e9076ae0bfd88c05c4f2badac9c49
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34633
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>