omap4xxx: Fix aliasing violation

Fix violation of aliasing rules

Change-Id: Ifc8a7c362dd923224a20d1658db052356c4cb7d9
Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>
omap4xxx: Fix aliasing violations, optimize

Fix some violations of aliasing rules and optimize the code while at it:
There's no reason to use size_t/ssize_t (typically 64-bit values) for
the size of objects in pixels.

Change-Id: I0af70a2847f070754b734e82c6f76fe01d0ea298
Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>