net: sfc: avoid -Wtype-limits warning

When building with -Wextra, we get a harmless warning from the
EFX_EXTRACT_OWORD32 macro:

ethernet/sfc/farch.c: In function 'efx_farch_test_registers':
ethernet/sfc/farch.c:119:30: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
ethernet/sfc/farch.c:124:144: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
ethernet/sfc/farch.c:124:392: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
ethernet/sfc/farch.c:124:731: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]

The macro and the caller are both correct, but we can avoid the
warning by changing the index variable to a signed type.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Bert Kenward <bkenward@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/farch.c

@@ -104,7 +104,8 @@ int efx_farch_test_registers(struct efx_nic *efx,
 			     const struct efx_farch_register_test *regs,
 			     size_t n_regs)
 {
-	unsigned address = 0, i, j;
+	unsigned address = 0;
+	int i, j;
 	efx_oword_t mask, imask, original, reg, buf;
 
 	for (i = 0; i < n_regs; ++i) {