staging: r8188eu: fix a memory leak in rtw_wx_read32()

Free "ptmp" before returning -EINVAL.

Fixes: 2b42bd58 ("staging: r8188eu: introduce new os_dep dir for RTL8188eu driver")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20211109114935.GC16587@kili


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>