mfd: Fix memory leak in ab3100_otp_probe

In current implementation, there is a memory leak if ab3100_otp_read fail.
And in the case of ab3100_otp_init_debugfs fail, it does not properly remove
sysfs entries.
This patch properly handle above failure cases.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>