media: pt1: fix logic when pt1_nr_tables is zero or negative

pt1_nr_tables is a modprobe parameter. The way the logic
handles it, it can't be negative. However, user can
set it to zero.

If set to zero, however, it will cause troubles at
pt1_init_tables(), as reported by smatch:
	drivers/media/pci/pt1/pt1.c:468 pt1_init_tables() error: uninitialized symbol 'first_pfn'.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/pci/pt1/pt1.c

@@ -116,8 +116,8 @@ static u32 pt1_read_reg(struct pt1 *pt1, int reg)
 	return readl(pt1->regs + reg * 4);
 }
 
-static int pt1_nr_tables = 8;
-module_param_named(nr_tables, pt1_nr_tables, int, 0);
+static unsigned int pt1_nr_tables = 8;
+module_param_named(nr_tables, pt1_nr_tables, uint, 0);
 
 static void pt1_increment_table_count(struct pt1 *pt1)
 {
@@ -443,6 +443,9 @@ static int pt1_init_tables(struct pt1 *pt1)
 	int i, ret;
 	u32 first_pfn, pfn;
 
+	if (!pt1_nr_tables)
+		return 0;
+
 	tables = vmalloc(sizeof(struct pt1_table) * pt1_nr_tables);
 	if (tables == NULL)
 		return -ENOMEM;
@@ -450,12 +453,10 @@ static int pt1_init_tables(struct pt1 *pt1)
 	pt1_init_table_count(pt1);
 
 	i = 0;
-	if (pt1_nr_tables) {
 	ret = pt1_init_table(pt1, &tables[0], &first_pfn);
 	if (ret)
 		goto err;
 	i++;
-	}
 
 	while (i < pt1_nr_tables) {
 		ret = pt1_init_table(pt1, &tables[i], &pfn);