avr32: fix 'undefined reference to `___copy_from_user'

avr32 builds fail with:

arch/avr32/kernel/built-in.o: In function `arch_ptrace':
(.text+0x650): undefined reference to `___copy_from_user'
arch/avr32/kernel/built-in.o:(___ksymtab+___copy_from_user+0x0): undefined
reference to `___copy_from_user'
kernel/built-in.o: In function `proc_doulongvec_ms_jiffies_minmax':
(.text+0x5dd8): undefined reference to `___copy_from_user'
kernel/built-in.o: In function `proc_dointvec_minmax_sysadmin':
sysctl.c:(.text+0x6174): undefined reference to `___copy_from_user'
kernel/built-in.o: In function `ptrace_has_cap':
ptrace.c:(.text+0x69c0): undefined reference to `___copy_from_user'
kernel/built-in.o:ptrace.c:(.text+0x6b90): more undefined references to
`___copy_from_user' follow

Fixes: 8630c322

 ("avr32: fix copy_from_user()")
Cc: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Havard Skinnemoen <hskinnemoen@gmail.com>
Acked-by: Hans-Christian Noren Egtvedt <egtvedt@samfundet.no>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>