msm: camera: Allow cmd buffer size to be equal to length

Sum of cmd buffer offset and its size can be equal to allocated
length by the kernel. Earlier, passing cmd buffer size equal to
kmd length was causing unit test to fail.

Change-Id: I7bca5a3a97321e403e6aa39fff2fe65b4cc624c3
Signed-off-by: Mukund Madhusudan Atre <matre@codeaurora.org>