power: bq24190_charger: suppress build warning

This patch fixes following build warning:

In file included from include/linux/printk.h:261:0,
                 from include/linux/kernel.h:13,
                 from include/linux/list.h:8,
                 from include/linux/module.h:9,
                 from drivers/power/bq24190_charger.c:11:
drivers/power/bq24190_charger.c: In function ‘bq24190_irq_handler_thread’:
include/linux/dynamic_debug.h:86:20: warning: ‘ss_reg’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   __dynamic_dev_dbg(&descriptor, dev, fmt, \
                    ^
drivers/power/bq24190_charger.c:1211:5: note: ‘ss_reg’ was declared here
  u8 ss_reg, f_reg;
     ^
In file included from include/linux/printk.h:261:0,
                 from include/linux/kernel.h:13,
                 from include/linux/list.h:8,
                 from include/linux/module.h:9,
                 from drivers/power/bq24190_charger.c:11:
include/linux/dynamic_debug.h:86:20: warning: ‘f_reg’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   __dynamic_dev_dbg(&descriptor, dev, fmt, \
                    ^
drivers/power/bq24190_charger.c:1211:13: note: ‘f_reg’ was declared here
  u8 ss_reg, f_reg;

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>