parisc: prefer _THIS_IP_ and _RET_IP_ statement expressions

As part of the effort to reduce the code duplication between _THIS_IP_
and current_text_addr(), let's consolidate callers of
current_text_addr() to use _THIS_IP_.

Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Helge Deller <deller@gmx.de>