ARM: 8158/1: LLVMLinux: use static inline in ARM ftrace.h

ARM: 8158/1: LLVMLinux: use static inline in ARM ftrace.h

With compilers which follow the C99 standard (like modern versions of gcc and
clang), "extern inline" does the wrong thing (emits code for an externally
linkable version of the inline function). In this case using static inline
and removing the NULL version of return_address in return_address.c does
the right thing.

Signed-off-by: Behan Webster <behanw@converseincode.com>
Reviewed-by: Mark Charlebois <charlebm@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
(cherry picked from commit aeea3592a13bf12861943e44fc48f1f270941f8d)