staging: rtl8188eu: Fix potential NULL pointer dereference of kcalloc

hwxmits is allocated via kcalloc and not checked for failure before its
dereference. The patch fixes this problem by returning error upstream
in rtl8723bs, rtl8188eu.

Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Acked-by: Mukesh Ojha <mojha@codeaurora.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>