leds: is31fl32xx: Fix missing error code in is31fl32xx_parse_dt()

leds: is31fl32xx: Fix missing error code in is31fl32xx_parse_dt()

The error code is missing in this code scenario, add the error code
'-EINVAL' to the return value 'ret'.

Eliminate the follow smatch warning:

drivers/leds/leds-is31fl32xx.c:388 is31fl32xx_parse_dt() warn: missing
error code 'ret'.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Fixes: 9d7cffaf99f5 ("leds: Add driver for the ISSI IS31FL32xx family of LED controllers")
Acked-by: David Rivshin <drivshin@allworx.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>