hw-breakpoints: Fix build warnings with clang

kbuild test robot reported some build warnings in the hw_breakpoint
code when compiled with clang[1]. Some of them were introduced by the
recent powerpc change to add arch_reserve_bp_slot() and
arch_release_bp_slot(). Fix them all.

kernel/events/hw_breakpoint.c:71:12: warning: no previous prototype for function 'hw_breakpoint_weight'
kernel/events/hw_breakpoint.c:216:12: warning: no previous prototype for function 'arch_reserve_bp_slot'
kernel/events/hw_breakpoint.c:221:13: warning: no previous prototype for function 'arch_release_bp_slot'
kernel/events/hw_breakpoint.c:228:13: warning: no previous prototype for function 'arch_unregister_hw_breakpoint'

[1]: https://lore.kernel.org/linuxppc-dev/[e-mail]/

Fixes: 29da4f91c0c1 ("powerpc/watchpoint: Don't allow concurrent perf and ptrace events")
Reported-by: kbuild test robot <[e-mail]>
Signed-off-by: Ravi Bangoria <[e-mail]>
[mpe: Drop extern, flesh out change log, add Fixes tag]
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/include/asm/hw_breakpoint.h

···
 						unsigned long val, void *data);
 int arch_install_hw_breakpoint(struct perf_event *bp);
 void arch_uninstall_hw_breakpoint(struct perf_event *bp);
-int arch_reserve_bp_slot(struct perf_event *bp);
-void arch_release_bp_slot(struct perf_event *bp);
-void arch_unregister_hw_breakpoint(struct perf_event *bp);
 void hw_breakpoint_pmu_read(struct perf_event *bp);
 extern void flush_ptrace_hw_breakpoint(struct task_struct *tsk);
 

include/linux/hw_breakpoint.h

···
 extern int dbg_release_bp_slot(struct perf_event *bp);
 extern int reserve_bp_slot(struct perf_event *bp);
 extern void release_bp_slot(struct perf_event *bp);
+int hw_breakpoint_weight(struct perf_event *bp);
+int arch_reserve_bp_slot(struct perf_event *bp);
+void arch_release_bp_slot(struct perf_event *bp);
+void arch_unregister_hw_breakpoint(struct perf_event *bp);
 
 extern void flush_ptrace_hw_breakpoint(struct task_struct *tsk);