Currently we request the irq when probing, but never free it. So after
unbind ec driver, this irq will be left requested, which would break
the next bind:

[ 2683.338437] genirq: Flags mismatch irq 64. 00002008 (chromeos-ec) vs. 00002008 (chromeos-ec)
[ 2683.338591] cros-ec-spi spi5.0: request irq 64: error -16
[ 2683.338610] cros-ec-spi spi5.0: cannot register EC
[ 2683.338656] cros-ec-spi: probe of spi5.0 failed with error -16
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>