staging: ks7010: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1].

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-throughSigned-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200727190417.GA29944@embeddedorSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/ks7010/ks_wlan_net.c

@@ -426,16 +426,16 @@ static int ks_wlan_set_rate(struct net_device *dev,
 					priv->reg.rate_set.body[3] =
 					    TX_RATE_11M;
 					i++;
-					/* fall through */
+					fallthrough;
 				case 5500000:
 					priv->reg.rate_set.body[2] = TX_RATE_5M;
 					i++;
-					/* fall through */
+					fallthrough;
 				case 2000000:
 					priv->reg.rate_set.body[1] =
 					    TX_RATE_2M | BASIC_RATE;
 					i++;
-					/* fall through */
+					fallthrough;
 				case 1000000:
 					priv->reg.rate_set.body[0] =
 					    TX_RATE_1M | BASIC_RATE;
@@ -491,17 +491,17 @@ static int ks_wlan_set_rate(struct net_device *dev,
 					priv->reg.rate_set.body[11] =
 					    TX_RATE_54M;
 					i++;
-					/* fall through */
+					fallthrough;
 				case 48000000:
 					priv->reg.rate_set.body[10] =
 					    TX_RATE_48M;
 					i++;
-					/* fall through */
+					fallthrough;
 				case 36000000:
 					priv->reg.rate_set.body[9] =
 					    TX_RATE_36M;
 					i++;
-					/* fall through */
+					fallthrough;
 				case 24000000:
 				case 18000000:
 				case 12000000:
@@ -578,17 +578,17 @@ static int ks_wlan_set_rate(struct net_device *dev,
 						    TX_RATE_6M | BASIC_RATE;
 						i++;
 					}
-					/* fall through */
+					fallthrough;
 				case 5500000:
 					priv->reg.rate_set.body[2] =
 					    TX_RATE_5M | BASIC_RATE;
 					i++;
-					/* fall through */
+					fallthrough;
 				case 2000000:
 					priv->reg.rate_set.body[1] =
 					    TX_RATE_2M | BASIC_RATE;
 					i++;
-					/* fall through */
+					fallthrough;
 				case 1000000:
 					priv->reg.rate_set.body[0] =
 					    TX_RATE_1M | BASIC_RATE;