regulator: gpio: Fix the out-of-bounds access to drvdata::gpiods

In the Linux kernel, the following vulnerability has been resolved:

regulator: gpio: Fix the out-of-bounds access to drvdata::gpiods

drvdata::gpiods is supposed to hold an array of 'gpio_desc' pointers. But the memory is allocated for only one pointer. This will lead to out-of-bounds access later in the code if 'config::ngpios' is > 1. So fix the code to allocate enough memory to hold 'config::ngpios' of GPIO descriptors.

While at it, also move the check for memory allocation failure to be below the allocation to make it more readable.