ARM: tegra: transformer: Drop reg-shift for Tegra HS UART

When the Tegra High-Speed UART is used instead of the regular UART, the
reg-shift property is implied from the compatible string and should not
be explicitly listed.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>