When optional clock requesting fails, the main clock is still up and running,
we should shut it down in such caee.

Fixes: 560ee7e9 ("spi: dw: Add support for an optional interface clock")
Cc: Phil Edworthy <phil.edworthy@renesas.com>
Cc: Gareth Williams <gareth.williams.jx@renesas.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Gareth Williams <gareth.williams.jx@renesas.com>
Link: https://lore.kernel.org/r/20190710114243.30101-1-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>