qspi: t210: Use dev_read calls to get FDT data like base, freq

This Tegra QSPI driver hadn't been brought up to date with how
DM drivers are fetching data from the FDT now, and was pulling
in bogus data for base, max freq, etc. Fixed ofdata_to_platdata
to work the same way it does in the tegra114 SPI driver, using
dev_read_ functions.

Signed-off-by: Tom Warren <twarren@nvidia.com>