staging: rtl8712: r8712_os_recvbuf_resource_alloc(): Change return values

staging: rtl8712: r8712_os_recvbuf_resource_alloc(): Change return values

Change return values of r8712_os_recvbuf_resource_alloc from
_SUCCESS/_FAIL to 0/-ENOMEM respectively.
Modify check at call site to check for non-zero return value instead of
_FAIL. Thereafter remove variable at call site that stored the return
value and perform the check directly.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190802064212.30476-4-nishkadg.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>