Blackfin arch: explicit add a might sleep to gpio_free

According to the documentation gpio_free should only be called from task
context only.  To make this more explicit add a might sleep to all
implementations.

This patch changes the gpio_free implementations for the blackfin
architecture.
Signed-off-by: Uwe Kleine-Koenig <ukleinek@strlen.de>
Cc: David Brownell <david-b@pacbell.net>
Acked-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/blackfin/kernel/bfin_gpio.c

@@ -1081,6 +1081,8 @@ void bfin_gpio_free(unsigned gpio)
 	if (check_gpio(gpio) < 0)
 		return;
 
+	might_sleep();
+
 	local_irq_save_hw(flags);
 
 	if (unlikely(!(reserved_gpio_map[gpio_bank(gpio)] & gpio_bit(gpio)))) {