staging: pi433: rf69.c style fix - code indent should use tabs

This patch fixes the following checkpatch.pl error:

ERROR: code indent should use tabs where possible

in rf69.c file as requested by TODO file.

Additionally some style warnings remain valid here and could be fixed by
another patch.
Signed-off-by: Marcin Ciupak <marcin.s.ciupak@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>