[MIPS] Use kallsyms_lookup_size_offset() instead of kallsyms_lookup()

This new routine doesn't lookup for symbol names. So we needn't
to pass any char buffers or pointer since we don't care about
names.

Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>