leds-ss4200: Check pci_enable_device return

pci_enable_result is defined using the __must_check macro but
leds-ss4200 is not checking the return value.

Signed-off-by: Javier Martinez Canillas <martinez.javier@gmail.com>
Signed-off-by: Dave Hansen <dave@sr71.net>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>