[media] exynos4-is: fimc-is: Unmap region obtained by of_iomap()

Free memory mapping, if fimc_is_probe is not successful.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>