leds: Fix potential leds-gpio oops

Call gpio_cansleep only after gpio_request succeeded avoiding an
oops.

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>