The PHY configuration is stored in an opaque "config" field, but when
allocating the structure, its proper size needs to be known. In the case
of UTMI, the proper structure is tegra_utmip_config of which a local
variable already exists, so we can use that to obtain the size from.

Fixes the following warning from the sparse checker:

	drivers/usb/phy/phy-tegra-usb.c:882:17: warning: expression using sizeof(void)

Fixes: 81d5dfe6 (usb: phy: tegra: Read UTMIP parameters from device tree)
Cc: stable@vger.kernel.org
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>