spi: designware: delete premature free_irq

Free_irq is not needed if there has been no request_irq.  Free_irq is
removed from both the probe and remove functions.  The correct request_irq
and free_irq appear to be in the add_host and remove_host functions in
spi-dw.c.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/

)

// <smpl>
@@
expression e;
@@

*e = platform_get_irq(...);
... when != request_irq(e,...)
*free_irq(e,...)
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Mark Brown <broonie@linaro.org>