phy: exynos5-usbdrd: Fix off-by-one valid value checking for args->args[0]

Current code uses args->args[0] as array subscript of phy_drd->phys[].
So the valid value range for args->args[0] is 0 ... EXYNOS5_DRDPHYS_NUM - 1.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed by: Vivek Gautam <gautam.vivek@samsung.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>