drivers/leds/leds-gpio.c: use gpio_get_value_cansleep() when initializing

I get the following warning:

------------[ cut here ]------------
WARNING: at drivers/gpio/gpiolib.c:1559 __gpio_get_value+0x90/0x98()
Modules linked in:
Call Trace:
[<ffffffff81440950>] dump_stack+0x8/0x34
[<ffffffff81141478>] warn_slowpath_common+0x78/0xa0
[<ffffffff812f0958>] __gpio_get_value+0x90/0x98
[<ffffffff81434f04>] create_gpio_led+0xdc/0x194
[<ffffffff8143524c>] gpio_led_probe+0x290/0x36c
[<ffffffff8130e8b0>] driver_probe_device+0x78/0x1b0
[<ffffffff8130eaa8>] __driver_attach+0xc0/0xc8
[<ffffffff8130d7ac>] bus_for_each_dev+0x64/0xb0
[<ffffffff8130e130>] bus_add_driver+0x1c8/0x2a8
[<ffffffff8130f100>] driver_register+0x90/0x180
[<ffffffff81100438>] do_one_initcall+0x38/0x160

---[ end trace ee38723fbefcd65c ]---

My GPIOs are on an I2C port expander, so we must use the *_cansleep()
variant of the GPIO functions.  This is was not being done in
create_gpio_led().

We can change gpio_get_value() to gpio_get_value_cansleep() because it is
only called from the platform_driver probe function, which is a context
where we can sleep.

Only tested on my gpio_cansleep() system, but it seems safe for all
systems.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Acked-by: Trent Piepho <tpiepho@gmail.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>