clk: si5351: Wait for bit clear after PLL reset

clk: si5351: Wait for bit clear after PLL reset

Documentation states that SI5351_PLL_RESET_B and SI5351_PLL_RESET_A bits
are self clearing bits, so wait until they are cleared before
continuing.
This fixes a case when the clock doesn't come up properly after a PLL
reset. It worked properly when the frequency was below 900MHz, but with
900MHz it only works when we are waiting for the bit to clear.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20201130091033.1687-1-s.hauer@pengutronix.de
Signed-off-by: Stephen Boyd <sboyd@kernel.org>