drm/tegra: fix compile w/ CONFIG_DYNAMIC_DEBUG

With CONFIG_DYNAMIC_DEBUG=y, the following compile error occurs:

drivers/gpu/drm/tegra/mipi-phy.c: In function ‘mipi_dphy_timing_validate’:
drivers/gpu/drm/tegra/mipi-phy.c:69:11: error: ‘EINVAL’ undeclared (first use in this function)
drivers/gpu/drm/tegra/mipi-phy.c:69:11: note: each undeclared identifier is reported only once for each function it appears in

Fix this by directly including the header that defines EINVAL.

Fixes: dec72739 ("drm/tegra: Add DSI support")
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>