powerpc: Fix 32-bit frames for signals delivered when transactional

Commit d31626f7

 ("powerpc: Don't corrupt transactional state when
using FP/VMX in kernel") introduced a bug where the uc_link and uc_regs
fields of the ucontext_t that is created to hold the transactional
values of the registers in a 32-bit signal frame didn't get set
correctly.  The reason is that we now clear the MSR_TS bits in the MSR
in save_tm_user_regs(), before the code that sets uc_link and uc_regs.
To fix this, we move the setting of uc_link and uc_regs into the same
if statement that selects whether to call save_tm_user_regs() or
save_user_regs().

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>