gma500: clean up error handling in init

gma500: clean up error handling in init

The main problem with this error handling was that it didn't clean up if
i2c_add_numbered_adapter() failed.  This code is pretty old, and doesn't
match with today's checkpatch.pl standards so I took the opportunity to
tidy it up a bit.  I changed the NULL comparison, and removed the
WARNING message if kzalloc() fails and updated the label names.

Fixes: 1b082ccf5901 ("gma500: Add Oaktrail support")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/X8ikkAqZfnDO2lu6@mwanda