tracing: make ftrace_likely_update() declaration visible

This function is only used when CONFIG_TRACE_BRANCH_PROFILING is set and
DISABLE_BRANCH_PROFILING is not set, and the declaration is hidden
behind this combination of tests.

But that causes a warning when building with CONFIG_TRACING_BRANCHES,
since that sets DISABLE_BRANCH_PROFILING for the tracing code, and the
declaration is thus hidden:

  kernel/trace/trace_branch.c:205:6: error: no previous prototype for 'ftrace_likely_update' [-Werror=missing-prototypes]

Move the declaration out of the #ifdef to avoid the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>