powerpc/signal32: Convert restore_[tm]_user_regs() to user access block

Convert restore_user_regs() and restore_tm_user_regs()
to use user_access_read_begin/end blocks.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/181adf15a6f644efcd1aeafb355f3578ff1b6bc5.1616151715.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/ptrace.h

@@ -245,7 +245,7 @@ static inline bool trap_norestart(struct pt_regs *regs)
 	return regs->trap & 0x10;
 }
 
-static inline void set_trap_norestart(struct pt_regs *regs)
+static __always_inline void set_trap_norestart(struct pt_regs *regs)
 {
 	regs->trap |= 0x10;
 }