staging: rtl8192u: null check the kzalloc

staging: rtl8192u: null check the kzalloc

In rtl8192_init_priv_variable allocation for priv->pFirmware may fail,
so a null check is necessary.priv->pFirmware is accessed later in
rtl8192_adapter_start. I added the check and made appropriate changes
to propagate the errno to the caller.

Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Link: https://lore.kernel.org/r/20190731141925.29268-1-navid.emamdoost@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>