drm/etnaviv: fix missing unlock on error in etnaviv_iommuv1_context_alloc()

Add the missing unlock before return from function etnaviv_iommuv1_context_alloc()
in the error handling case.

Fixes: 27b67278 ("drm/etnaviv: rework MMU handling")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

drivers/gpu/drm/etnaviv/etnaviv_iommu.c

@@ -140,8 +140,10 @@ etnaviv_iommuv1_context_alloc(struct etnaviv_iommu_global *global)
 	}
 
 	v1_context = kzalloc(sizeof(*v1_context), GFP_KERNEL);
-	if (!v1_context)
+	if (!v1_context) {
+		mutex_unlock(&global->lock);
 		return NULL;
+	}
 
 	v1_context->pgtable_cpu = dma_alloc_wc(global->dev, PT_SIZE,
 					       &v1_context->pgtable_dma,