mfd/asic3: fix asic3_mfd_probe return value

In commit 4f304245 "mfd: Set asic3 DS1WM clock_rate", a possible
path through asic3_mfd_probe was introduced that would lead to
an unpredictable return value, if everything succeeds but there
are pdata->leds is NULL. This was reported correctly by gcc.

Without this patch, building magician_defconfig results in:

drivers/mfd/asic3.c: In function 'asic3_mfd_probe':
drivers/mfd/asic3.c:940:2: warning: 'ret' may be used uninitialized in this function [-Wuninitialized]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Parsons <lost.distance@yahoo.com>
Cc: Philipp Zabel <philipp.zabel@gmail.com>
Cc: Samuel Ortiz <sameo@linux.intel.com>