drivers: misc: ti-st: fix potential race if st_kim_start fails

If st_kim_start() fails registered protocols should be removed. This is
done by calling st_reg_complete(), which as comment states is called
with spin lock held. But in st_register() when st_kim_start fails it
is called without holding spin lock, creating possibility of concurrent
access to st_gdata data members.
Hold spin lock while calling st_reg_complete if st_kim_start() fails.

Signed-off-by: Oleksandr Kozaruk <oleksandr.kozaruk@globallogic.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>