soc: fsl: cpm1: qmc: Add missing spinlock comment

checkpatch.pl raises the following issue
  CHECK: spinlock_t definition without comment

Add the missing comments.
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20240808071132.149251-23-herve.codina@bootlin.comSigned-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>

drivers/soc/fsl/qe/qmc.c

@@ -196,7 +196,7 @@ struct qmc_chan {
 	u64	rx_ts_mask;
 	bool is_reverse_data;
 
-	spinlock_t	tx_lock;
+	spinlock_t	tx_lock; /* Protect Tx related data */
 	cbd_t __iomem *txbds;
 	cbd_t __iomem *txbd_free;
 	cbd_t __iomem *txbd_done;
@@ -204,7 +204,7 @@ struct qmc_chan {
 	u64	nb_tx_underrun;
 	bool	is_tx_stopped;
 
-	spinlock_t	rx_lock;
+	spinlock_t	rx_lock; /* Protect Rx related data */
 	cbd_t __iomem *rxbds;
 	cbd_t __iomem *rxbd_free;
 	cbd_t __iomem *rxbd_done;