Identical implementations of PTRACE_POKEDATA go into generic_ptrace_pokedata()
function.

AFAICS, fix bug on xtensa where successful PTRACE_POKEDATA will nevertheless
return EPERM.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>