spi: spi-ep93xx: Prepare clock before using it

spi: spi-ep93xx: Prepare clock before using it

Use clk_prepare_enable()/clk_disable_unprepare() in preparation for switch
to Common Clock Framework, otherwise the following is visible:

WARNING: CPU: 0 PID: 1 at drivers/clk/clk.c:1011 clk_core_enable+0x9c/0xbc
Enabling unprepared ep93xx-spi.0
...
Hardware name: Cirrus Logic EDB9302 Evaluation Board
...
clk_core_enable
clk_core_enable_lock
ep93xx_spi_prepare_hardware
__spi_pump_messages
__spi_sync
spi_sync
spi_sync_transfer.constprop.0
regmap_spi_write
_regmap_raw_write_impl
_regmap_bus_raw_write
_regmap_update_bits
regmap_update_bits_base
cs4271_component_probe
snd_soc_component_probe
soc_probe_component
snd_soc_bind_card
edb93xx_probe
...
spi_master spi0: failed to prepare transfer hardware: -108

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210726140001.24820-3-nikita.shubin@maquefel.me
Signed-off-by: Mark Brown <broonie@kernel.org>