eth: bnxt: fix warning for define in struct_group

Fix C=1 warning with sparse 0.6.4:

drivers/net/ethernet/broadcom/bnxt/bnxt.c: note: in included file:
drivers/net/ethernet/broadcom/bnxt/bnxt_dcb.h:30:1: warning: directive in macro's argument list

Don't put defines in a struct_group().

Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20230727190726.1859515-3-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>