staging: rtl8723bs: Fix an error handling path

'ret' is known to be 0 at this point. It must be set to -ENOMEM if a
memory allocation occurs.

Fixes: 554c0a3a ("staging: Add rtl8723bs sdio wifi driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/a9533d1594900152e1e64e9f09e54240e3b7062a.1624177169.git.christophe.jaillet@wanadoo.fr


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