scripts/tiny/ksize: Fix for more recent kernels

In the past kernel built object files were named 'built-in.o'.
Nowadays it is 'built-in.a'.

The script is modified to work with both.  I expect
it will not happen that there are built-in.a and built-in.o
files in the same kernel.

Signed-off-by: Jan Vermaete <jan.vermaete@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>