phy: exynos-mipi-video: fix check on array index

The phys array is of size EXYNOS_MIPI_PHYS_NUM. Trying to access the
index EXYNOS_MIPI_PHYS_NUM should return an error.

Fixes: 069d2e26

 "phy: Add driver for Exynos MIPI CSIS/DSIM DPHYs"

Signed-off-by: Antoine Ténart <antoine.tenart@free-electrons.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>