sparc64: Fix perf_arch_get_caller_regs().

After b0f82b81

 ("perf: Drop the skip
argument from perf_arch_fetch_regs_caller") the build broke on sparc64
due to the lack of a module symbol export of __perf_arch_fetch_caller_regs.

But that assembler helper can actually be complete eliminated now that
the semantics of this interface have been greatly simplified.

Signed-off-by: David S. Miller <davem@davemloft.net>