pda_power: Check and handle return value of set_irq_wake

The recent change in commit 2db87321
forces the calls enable_irq_wake() and disable_irq_wake() to
be balanced. But if in pda_power_suspend() the call to
enable_irq_wake() fails (because attached gpio cannot wake
up the CPU), the corresponding disable_irq_wake will WARN().
Fix it by storing success/failure of enable_irq_wake().

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>