ARC: perf: don't bail setup if pct irq missing in device-tree

Current code inadventely bails if hardware supports sampling/overflow
interrupts, but the irq is missing from device tree.

|
| # perf stat -e cycles,instructions,major-faults,minor-faults ../hackbench
| Running with 10 groups 400 process
| Time: 0.921
|
| Performance counter stats for '../hackbench':
|
|   <not supported>      cycles
|   <not supported>      instructions
|                 0      major-faults
|              8679      minor-faults

This need not be as we can still do simple counting based perf stat.
This unborks perf on HSDK-4xD

Cc: <stable@vger.kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/kernel/perf_event.c

@@ -562,7 +562,7 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
 {
 	struct arc_reg_pct_build pct_bcr;
 	struct arc_reg_cc_build cc_bcr;
-	int i, has_interrupts;
+	int i, has_interrupts, irq;
 	int counter_size;	/* in bits */
 
 	union cc_name {
@@ -637,13 +637,7 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
 		.attr_groups	= arc_pmu->attr_groups,
 	};
 
-	if (has_interrupts) {
-		int irq = platform_get_irq(pdev, 0);
-
-		if (irq < 0) {
-			pr_err("Cannot get IRQ number for the platform\n");
-			return -ENODEV;
-		}
+	if (has_interrupts && (irq = platform_get_irq(pdev, 0) >= 0)) {
 
 		arc_pmu->irq = irq;
 
@@ -652,9 +646,9 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
 				   this_cpu_ptr(&arc_pmu_cpu));
 
 		on_each_cpu(arc_cpu_pmu_irq_init, &irq, 1);
-
-	} else
+	} else {
 		arc_pmu->pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
+	}
 
 	/*
 	 * perf parser doesn't really like '-' symbol in events name, so let's