netxen_nic: Replace fake flex-array with flexible-array member

Zero-length arrays as fake flexible arrays are deprecated and we are
moving towards adopting C99 flexible-array members instead.

Transform zero-length array into flexible-array member in struct
nx_cardrsp_rx_ctx_t.

Address the following warnings found with GCC-13 and
-fstrict-flex-arrays=3 enabled:
drivers/net/ethernet/qlogic/netxen/netxen_nic_ctx.c:361:26: warning: array subscript <unknown> is outside array bounds of ‘char[0]’ [-Warray-bounds=]
drivers/net/ethernet/qlogic/netxen/netxen_nic_ctx.c:372:25: warning: array subscript <unknown> is outside array bounds of ‘char[0]’ [-Warray-bounds=]

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
routines on memcpy() and help us make progress towards globally
enabling -fstrict-flex-arrays=3 [1].

Link: KSPP/linux#21
Link: KSPP/linux#265
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
Signed-off-by: Gustavo A. R. Silva <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://lore.kernel.org/r/ZAZ57I6WdQEwWh7v@work
Signed-off-by: Jakub Kicinski <[email protected]>

Author: GustavoARSilva

drivers/net/ethernet/qlogic/netxen/netxen_nic.h

@@ -854,7 +854,7 @@ typedef struct {
 	   The following is packed:
 	   - N cardrsp_rds_rings
 	   - N cardrs_sds_rings */
-	char data[0];
+	char data[];
 } nx_cardrsp_rx_ctx_t;
 
 #define SIZEOF_HOSTRQ_RX(HOSTRQ_RX, rds_rings, sds_rings)	\