gpio: fix memory leak in gpiod_request_commit()

Since commit 1f2bcb8c ("gpio: protect the descriptor label with
SRCU"), desc_set_label() already allocates memory for the label, so there
is no need to allocate it again. If we do, we leak it.

unreferenced object 0xffff0000c3e4d0c0 (size 32):
  comm "kworker/u16:4", pid 60, jiffies 4294894555
  hex dump (first 32 bytes):
    72 65 67 75 6c 61 74 6f 72 2d 63 61 6e 32 2d 73  regulator-can2-s
    74 62 79 00 00 00 ff ff ff ff ff ff eb db ff ff  tby.............
  backtrace (crc 2c3a0350):
    [<00000000e93c5cf4>] kmemleak_alloc+0x34/0x40
    [<0000000097a2657f>] __kmalloc_node_track_caller+0x2c4/0x524
    [<000000000dd1c057>] kstrdup+0x4c/0x98
    [<00000000b513a96a>] kstrdup_const+0x34/0x40
    [<000000008a7f0feb>] gpiod_request_commit+0xdc/0x358
    [<00000000fc71ad64>] gpiod_request+0xd8/0x204
    [<00000000fa24b091>] gpiod_find_and_request+0x170/0x780
    [<0000000086ecf92d>] gpiod_get_index+0x70/0xe0
    [<000000004aef97f9>] gpiod_get_optional+0x18/0x30
    [<00000000312f1b25>] reg_fixed_voltage_probe+0x58c/0xad8
    [<00000000e6f47635>] platform_probe+0xc4/0x198
    [<00000000cf78fbdb>] really_probe+0x204/0x5a8
    [<00000000e28d05ec>] __driver_probe_device+0x158/0x2c4
    [<00000000e4fe452b>] driver_probe_device+0x60/0x18c
    [<00000000479fcf5d>] __device_attach_driver+0x168/0x208
    [<000000007d389f38>] bus_for_each_drv+0x104/0x190

Fixes: 1f2bcb8c ("gpio: protect the descriptor label with SRCU")
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>
[Bartosz: tweaked the commit message]
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/gpio/gpiolib.c

@@ -2250,12 +2250,6 @@ static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
 	if (test_and_set_bit(FLAG_REQUESTED, &desc->flags))
 		return -EBUSY;
 
-	if (label) {
-		label = kstrdup_const(label, GFP_KERNEL);
-		if (!label)
-			return -ENOMEM;
-	}
-
 	/* NOTE:  gpio_request() can be called in early boot,
 	 * before IRQs are enabled, for non-sleeping (SOC) GPIOs.
 	 */