qbman_portal.c: Update BUG_ON() call in qbman_swp_mc_submit

With gcc-5.x we get a warning about the ambiguity of BUG_ON(!a != b) and
becomes BUG_ON((!a) != b).  In this case reading of the function leads to
us wanting to rewrite this as BUG_ON(a != b).

Cc: Prabhakar Kushwaha <prabhakar@freescale.com>
Cc: Geoff Thorpe <Geoff.Thorpe@freescale.com>
Cc: Haiying Wang <Haiying.Wang@freescale.com>
Cc: Roy Pledge <Roy.Pledge@freescale.com>
Cc: York Sun <yorksun@freescale.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: York Sun <yorksun@freescale.com>