sparc32: Remove uses of %g7 in memcpy implementation.

[ Upstream commit 21f74d36 ]

This is setting things up so that we can correct the return
value, so that it properly returns the original destination
buffer pointer.

Signed-off-by: David S. Miller <davem@davemloft.net>
Tested-by: Kjetil Oftedal <oftedal@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>