mwifiex: fix null derefs, mem leaks and trivia

This patch:
 - adds kfree() where necessary
 - prevents potential null dereferences
 - makes use of kfree_skb()
 - replaces -1 for failed kzallocs with -ENOMEM

Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>
Reviewed-by: Kiran Divekar <dkiran@marvell.com>
Tested-by: Amitkumar Karwar <akarwar@marvell.com>
Acked-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/mwifiex/scan.c b/drivers/net/wireless/mwifiex/scan.c
index 4968974..5c22860 100644
--- a/drivers/net/wireless/mwifiex/scan.c
+++ b/drivers/net/wireless/mwifiex/scan.c
@@ -2283,7 +2283,7 @@
 					GFP_KERNEL);
 	if (!scan_cfg_out) {
 		dev_err(adapter->dev, "failed to alloc scan_cfg_out\n");
-		return -1;
+		return -ENOMEM;
 	}
 
 	buf_size = sizeof(struct mwifiex_chan_scan_param_set) *
@@ -2292,7 +2292,7 @@
 	if (!scan_chan_list) {
 		dev_err(adapter->dev, "failed to alloc scan_chan_list\n");
 		kfree(scan_cfg_out);
-		return -1;
+		return -ENOMEM;
 	}
 
 	keep_previous_scan = false;
@@ -2491,7 +2491,7 @@
 				GFP_KERNEL);
 	if (!bss_new_entry) {
 		dev_err(adapter->dev, " failed to alloc bss_new_entry\n");
-		return -1;
+		return -ENOMEM;
 	}
 
 	for (idx = 0; idx < scan_rsp->number_of_sets && bytes_left; idx++) {
@@ -2881,7 +2881,7 @@
 	scan_cfg = kzalloc(sizeof(struct mwifiex_user_scan_cfg), GFP_KERNEL);
 	if (!scan_cfg) {
 		dev_err(adapter->dev, "failed to alloc scan_cfg\n");
-		return -1;
+		return -ENOMEM;
 	}
 
 	memcpy(scan_cfg->ssid_list[0].ssid, req_ssid->ssid,