staging: atomisp: remove enable_isp_irq function and add disable_isp_irq

Enable/Disable ISP irq is switched with "enable" parameter of
enable_isp_irq(). It would be better splited to two such as
enable_isp_irq()/disable_isp_irq().

But the enable_isp_irq() is no use in atomisp_cmd.c file.
So remove the enable_isp_irq() function and add
disable_isp_irq function only.

Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>