gpiolib: Separate GPIO_GET_LINEINFO_WATCH_IOCTL conditional

gpiolib: Separate GPIO_GET_LINEINFO_WATCH_IOCTL conditional

We already have two conditionals inside the outer one to check
if the command is GPIO_GET_LINEINFO_WATCH_IOCTL. I think it's
time to actually do what I have proposed in the first place, i.e.
to separate GPIO_GET_LINEINFO_WATCH_IOCTL from GPIO_GET_LINEINFO_IOCTL.
It's +13 LOCs, and surprisingly only +13 bytes of binary on x86_32,
but for the price of much better readability.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Link: https://lore.kernel.org/r/20200525194028.74236-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>