net: bnxt_ptp: fix compilation error

The Broadcom bnxt_ptp driver does not compile with GCC 11.2.2 when
CONFIG_WERROR is enabled. The following error is generated:

drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c: In function ‘bnxt_ptp_enable’:
drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c:400:43: error: array
subscript 255 is above array bounds of ‘struct pps_pin[4]’
[-Werror=array-bounds]
400 | ptp->pps_info.pins[pin_id].event = BNXT_PPS_EVENT_EXTERNAL;
| ~~~~~~~~~~~~~~~~~~^~~~~~~~
In file included from drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c:20:
drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h:75:24: note: while
referencing ‘pins’
75 | struct pps_pin pins[BNXT_MAX_TSIO_PINS];
| ^~~~
cc1: all warnings being treated as errors

This is due to the function ptp_find_pin() returning a pin ID of -1 when
a valid pin is not found and this error never being checked.
Change the TSIO_PIN_VALID() function to also check that a pin ID is not
negative and use this macro in bnxt_ptp_enable() to check the result of
the calls to ptp_find_pin() to return an error early for invalid pins.
This fixes the compilation error.

Cc: <[e-mail]>
Fixes: 9e518f25802c ("bnxt_en: 1PPS functions to configure TSIO pins")
Signed-off-by: Damien Le Moal <[e-mail]>
Reviewed-by: Michael Chan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c

···
 	struct bnxt_ptp_cfg *ptp = container_of(ptp_info, struct bnxt_ptp_cfg,
 						ptp_info);
 	struct bnxt *bp = ptp->bp;
-	u8 pin_id;
+	int pin_id;
 	int rc;
 
 	switch (rq->type) {
···
 		/* Configure an External PPS IN */
 		pin_id = ptp_find_pin(ptp->ptp_clock, PTP_PF_EXTTS,
 				      rq->extts.index);
+		if (!TSIO_PIN_VALID(pin_id))
+			return -EOPNOTSUPP;
 		if (!on)
 			break;
 		rc = bnxt_ptp_cfg_pin(bp, pin_id, BNXT_PPS_PIN_PPS_IN);
···
 		/* Configure a Periodic PPS OUT */
 		pin_id = ptp_find_pin(ptp->ptp_clock, PTP_PF_PEROUT,
 				      rq->perout.index);
+		if (!TSIO_PIN_VALID(pin_id))
+			return -EOPNOTSUPP;
 		if (!on)
 			break;
 

drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h

···
 	u8 state;
 };
 
-#define TSIO_PIN_VALID(pin) ((pin) < (BNXT_MAX_TSIO_PINS))
+#define TSIO_PIN_VALID(pin) ((pin) >= 0 && (pin) < (BNXT_MAX_TSIO_PINS))
 
 #define EVENT_DATA2_PPS_EVENT_TYPE(data2)				\
 	((data2) & ASYNC_EVENT_CMPL_PPS_TIMESTAMP_EVENT_DATA2_EVENT_TYPE)