clk: si5341: Wait for DEVICE_READY on startup

clk: si5341: Wait for DEVICE_READY on startup

The Si5341 datasheet warns that before accessing any other registers,
including the PAGE register, we need to wait for the DEVICE_READY register
to indicate the device is ready, or the process of the device loading its
state from NVM can be corrupted. Wait for DEVICE_READY on startup before
continuing initialization. This is done using a raw I2C register read
prior to setting up regmap to avoid any potential unwanted automatic PAGE
register accesses from regmap at this stage.

Fixes: 10c619dadb ("clk: Add Si5341/Si5340 driver")
Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Link: https://lore.kernel.org/r/20210325192643.2190069-3-robert.hancock@calian.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>