drivers: net: ldpaa_eth: Correct error handler for qbman_swp_acquire()

The zero value returned from qbman_swp_acquire() is an error
condition meaning no free buffer for allocation.

Signed-off-by: Ashish Kumar <Ashish.Kumar@nxp.com>
Signed-off-by: Kushwaha Prabhakar <prabhakar@freescale.com>
[YS: revised commit message]
Reviewed-by: York Sun <york.sun@nxp.com>
1 file changed