spi/bcm63xx-hsspi: keep pll clk enabled

[ Upstream commit 0fd85869c2a9c8723a98bc1f56a876e8383649f4 ]

If the pll clock needs to be enabled to get its rate, it will also need
to be enabled to provide it. So ensure it is kept enabled through the
lifetime of the device.

Fixes: 0d7412ed ("spi/bcm63xx-hspi: Enable the clock before calling clk_get_rate().")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>