sparc32: fix a braino in fault handling in csum_and_copy_..._user()

Fault handler used to make non-trivial calls, so it needed
to set a stack frame up. Used to be
save ... - grab a stack frame, old %o... become %i...
....
ret - go back to address originally in %o7, currently %i7
restore - switch to previous stack frame, in delay slot
Non-trivial calls had been gone since ab5e8b331244 and that code should
have become
retl - go back to address in %o7
clr %o0 - have return value set to 0
What it had become instead was
ret - go back to address in %i7 - return address of *caller*
clr %o0 - have return value set to 0
which is not good, to put it mildly - we forcibly return 0 from
csum_and_copy_{from,to}_iter() (which is what the call of that
thing had been inlined into) and do that without dropping the
stack frame of said csum_and_copy_..._iter(). Confuses the
hell out of the caller of csum_and_copy_..._iter(), obviously...

Reviewed-by: Sam Ravnborg <[e-mail]>
Fixes: ab5e8b331244 "sparc32: propagate the calling conventions change down to __csum_partial_copy_sparc_generic()"
Signed-off-by: Al Viro <[e-mail]>

arch/sparc/lib/checksum_32.S

···
  * we only bother with faults on loads... */
 
 cc_fault:
-	ret
+	retl
 	 clr	%o0