mmc: slot-gpio: Refactor mmc_gpio_alloc()

Refactor mmc_gpio_alloc() to drop unneeded indentation level
and double condition. This increases readability of the code.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210929111757.52625-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>