nvme-pci: check kstrtoint() return value in queue_count_set()

This patch avoids that the compiler complains about 'ret' being set
but not being used when building with W=1.

Fixes: 3b6592f70a ("nvme: utilize two queue maps, one for reads and one for writes") # v5.0-rc1
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/pci.c

@@ -157,6 +157,8 @@ static int queue_count_set(const char *val, const struct kernel_param *kp)
 	int n = 0, ret;
 
 	ret = kstrtoint(val, 10, &n);
+	if (ret)
+		return ret;
 	if (n > num_possible_cpus())
 		n = num_possible_cpus();