m32r: use generic current.h

Given that the arch does not add its own implementations, simply
use the asm-generic/current.h (generic-y) header instead of
duplicating code.

Link: http://lkml.kernel.org/r/1482896994-25863-1-git-send-email-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>