gpiolib: fix race condition for gdev->srcu

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

gpiolib: fix race condition for gdev->srcu

If two drivers were calling gpiochip_add_data_with_key(), one may be
traversing the srcu-protected list in gpio_name_to_desc(), meanwhile
other has just added its gdev in gpiodev_add_to_list_unlocked().
This creates a non-mutexed and non-protected timeframe, when one
instance is dereferencing and using &gdev->srcu, before the other
has initialized it, resulting in crash:

[ 4.935481] Unable to handle kernel paging request at virtual address ffff800272bcc000
[ 4.943396] Mem abort info:
[ 4.943400] ESR = 0x0000000096000005
[ 4.943403] EC = 0x25: DABT (current EL), IL = 32 bits
[ 4.943407] SET = 0, FnV = 0
[ 4.943410] EA = 0, S1PTW = 0
[ 4.943413] FSC = 0x05: level 1 translation fault
[ 4.943416] Data abort info:
[ 4.943418] ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
[ 4.946220] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 4.955261] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 4.955268] swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000038e6c000
[ 4.961449] [ffff800272bcc000] pgd=0000000000000000
[ 4.969203] , p4d=1000000039739003
[ 4.979730] , pud=0000000000000000
[ 4.980210] phandle (CPU): 0x0000005e, phandle (BE): 0x5e000000 for node "reset"
[ 4.991736] Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
...
[ 5.121359] pc : __srcu_read_lock+0x44/0x98
[ 5.131091] lr : gpio_name_to_desc+0x60/0x1a0
[ 5.153671] sp : ffff8000833bb430
[ 5.298440]
[ 5.298443] Call trace:
[ 5.298445] __srcu_read_lock+0x44/0x98
[ 5.309484] gpio_name_to_desc+0x60/0x1a0
[ 5.320692] gpiochip_add_data_with_key+0x488/0xf00
5.946419] ---[ end trace 0000000000000000 ]---

Move initialization code for gdev fields before it is added to
gpio_devices, with adjacent initialization code.
Adjust goto statements to reflect modified order of operations

[Bartosz: fixed a build issue, removed stray newline]