power: supply: cpcap-battery: Fix platform_get_irq_byname's error checking

The platform_get_irq_byname() function returns -1 if an error occurs.
zero or positive number on success. platform_get_irq_byname() error
checking for zero is not correct.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>