microblaze: Fix variable types to remove W=1 warning

This patch removes this warning:
arch/microblaze/kernel/signal.c: In function 'setup_rt_frame':
arch/microblaze/kernel/signal.c:177:3: warning: signed and unsigned type
in conditional expression [-Wsign-compare]
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

arch/microblaze/kernel/signal.c

@@ -158,7 +158,7 @@ static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
 {
 	struct rt_sigframe __user *frame;
 	int err = 0, sig = ksig->sig;
-	int signal;
+	unsigned long signal;
 	unsigned long address = 0;
 #ifdef CONFIG_MMU
 	pmd_t *pmdp;
@@ -174,7 +174,7 @@ static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
 		&& current_thread_info()->exec_domain->signal_invmap
 		&& sig < 32
 		? current_thread_info()->exec_domain->signal_invmap[sig]
-		: sig;
+		: (unsigned long)sig;
 
 	if (ksig->ka.sa.sa_flags & SA_SIGINFO)
 		err |= copy_siginfo_to_user(&frame->info, &ksig->info);