gpio: shared: fix memory leaks

On a Snapdragon X1 Elite laptop (Lenovo Yoga Slim 7x), kmemleak reports
three sets of:

unreferenced object 0xffff00080187f400 (size 1024):
comm "swapper/0", pid 1, jiffies 4294667327
hex dump (first 32 bytes):
58 bd 70 01 08 00 ff ff 58 bd 70 01 08 00 ff ff X.p.....X.p.....
00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 ................
backtrace (crc 1665d1f8):
kmemleak_alloc+0xf4/0x12c
__kmalloc_cache_noprof+0x370/0x49c
gpio_shared_make_ref+0x70/0x16c
gpio_shared_of_traverse+0x4e8/0x5f4
gpio_shared_of_traverse+0x200/0x5f4
gpio_shared_of_traverse+0x200/0x5f4
gpio_shared_of_traverse+0x200/0x5f4
gpio_shared_of_traverse+0x200/0x5f4
gpio_shared_init+0x34/0x1c4
do_one_initcall+0x50/0x280
kernel_init_freeable+0x290/0x33c
kernel_init+0x28/0x14c
ret_from_fork+0x10/0x20

unreferenced object 0xffff00080170c140 (size 8):
comm "swapper/0", pid 1, jiffies 4294667327
hex dump (first 8 bytes):
72 65 73 65 74 00 00 00 reset...
backtrace (crc fc24536):
kmemleak_alloc+0xf4/0x12c
__kmalloc_node_track_caller_noprof+0x3c4/0x584
kstrdup+0x4c/0xcc
gpio_shared_make_ref+0x8c/0x16c
gpio_shared_of_traverse+0x4e8/0x5f4
gpio_shared_of_traverse+0x200/0x5f4
gpio_shared_of_traverse+0x200/0x5f4
gpio_shared_of_traverse+0x200/0x5f4
gpio_shared_of_traverse+0x200/0x5f4
gpio_shared_init+0x34/0x1c4
do_one_initcall+0x50/0x280
kernel_init_freeable+0x290/0x33c
kernel_init+0x28/0x14c
ret_from_fork+0x10/0x20

Fix this by decrementing the reference count of each list entry rather than
only the first.

Fix verified on the same laptop.

Fixes: a060b8c511abb gpiolib: implement low-level, shared GPIO support
Signed-off-by: Daniel J Blueman <daniel@quora.org>
Link: https://patch.msgid.link/20260220093452.101655-1-daniel@quora.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>