mtd: docg3: off by one in doc_register_sysfs()

Smatch found a bug in the error handling:

	drivers/mtd/devices/docg3.c:1634 doc_register_sysfs()
	error: buffer overflow 'doc_sys_attrs' 4 <= 4

The problem is that if the very last device_create_file() fails, then we
are beyond the end of the array.  Actually, any time i == 3 then there
is a problem.  We can fix this an simplify the code at the same time by
moving the !ret conditions out of the for loops and using a goto
instead.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>