mwifiex: fix memory leak in mwifiex_save_hidden_ssid_channels()

mwifiex: fix memory leak in mwifiex_save_hidden_ssid_channels()

kmemleak reports memory leak in mwifiex_save_hidden_ssid_channels():

unreferenced object 0xffffffc0a2914780 (size 192):
  comm "ksdioirqd/mmc2", pid 2004, jiffies 4307182506 (age 820.684s)
  hex dump (first 32 bytes):
    00 06 47 49 4e 2d 32 67 01 03 c8 60 6c 03 01 40  ..GIN-2g...`l..@
    07 10 54 57 20 34 04 1e 64 05 24 84 03 24 95 04  ..TW 4..d.$..$..
  backtrace:
    [<ffffffc0003375f4>] create_object+0x164/0x2b4
    [<ffffffc0008e3530>] kmemleak_alloc+0x50/0x88
    [<ffffffc000335120>] __kmalloc_track_caller+0x1bc/0x264
    [<ffffffc00030899c>] kmemdup+0x38/0x64
    [<ffffffbffc2311cc>] mwifiex_fill_new_bss_desc+0x3c/0x130 [mwifiex]
    [<ffffffbffc22ee9c>] mwifiex_save_curr_bcn+0x4ec/0x640 [mwifiex]
    [<ffffffbffc22f45c>] mwifiex_handle_event_ext_scan_report+0x1d4/0x268 [mwifiex]
    [<ffffffbffc2375d0>] mwifiex_process_sta_event+0x378/0x898 [mwifiex]
    [<ffffffbffc224dc8>] mwifiex_process_event+0x1a8/0x1e8 [mwifiex]
    [<ffffffbffc2228f0>] mwifiex_main_process+0x258/0x534 [mwifiex]
    [<ffffffbffc258858>] 0xffffffbffc258858
    [<ffffffc00071ee90>] process_sdio_pending_irqs+0xf8/0x160
    [<ffffffc00071efdc>] sdio_irq_thread+0x9c/0x1a4
    [<ffffffc000240d08>] kthread+0xf4/0x100
    [<ffffffc0002043fc>] ret_from_fork+0xc/0x50
    [<ffffffffffffffff>] 0xffffffffffffffff

Signed-off-by: Ricky Liang <jcliang@chromium.org>
Acked-by: Amitkumar Karwar <akarwar@marvell.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>