staging: gpib: Add lower bound check for secondary address

Commit 9dde455 ("staging: gpib: Add GPIB common core driver")
from Sep 18, 2024 (linux-next), leads to the following Smatch static
checker warning:

	drivers/staging/gpib/common/gpib_os.c:541 dvrsp()
	warn: no lower bound on 'sad' rl='s32min-30'

The value -1 was introduced in user land to signify No secondary address
to the driver so that a lower bound check could be added.

This patch adds that check.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/linux-staging/4efd91f3-4259-4e95-a4e0-925853b98858@stanley.mountain/
Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20241207123410.28759-1-dpenkler@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: dpenkler

drivers/staging/gpib/common/gpib_os.c

@@ -536,7 +536,7 @@ int dvrsp(gpib_board_t *board, unsigned int pad, int sad,
 		return -1;
 	}
 
-	if (pad > MAX_GPIB_PRIMARY_ADDRESS || sad > MAX_GPIB_SECONDARY_ADDRESS) {
+	if (pad > MAX_GPIB_PRIMARY_ADDRESS || sad > MAX_GPIB_SECONDARY_ADDRESS || sad < -1) {
 		pr_err("gpib: bad address for serial poll");
 		return -1;
 	}