sparc64: Fix exception handling in UltraSPARC-III memcpy.

[ Upstream commit 0ede1c401332173ab0693121dc6cde04a4dbf131 ]

Mikael Pettersson reported that some test programs in the strace-4.18
testsuite cause an OOPS.

After some debugging it turns out that garbage values are returned
when an exception occurs, causing the fixup memset() to be run with
bogus arguments.

The problem is that two of the exception handler stubs write the
successfully copied length into the wrong register.

Fixes: ee841d0a ("sparc64: Convert U3copy_{from,to}_user to accurate exception reporting.")
Reported-by: Mikael Pettersson <mikpelinux@gmail.com>
Tested-by: Mikael Pettersson <mikpelinux@gmail.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>