staging: wlan-ng: replace strncpy() with strscpy()

Checkpatch suggests the use of strscpy() instead of strncpy().
The advantages are that it always adds a NUL terminator and it prevents
a read overflow if the src string is not properly terminated. One
potential disadvantage is that it doesn't zero pad the string like
strncpy() does.
In this code, strscpy() and strncpy() are equivalent and it does not
affect runtime behavior. The string is zeroed on the line before
using memset(). The resulting string was always NUL terminated and
PRISM2_USB_FWFILE is string literal "prism2_ru.fw" so it's NUL
terminated.
However, even though using strscpy() does not fix any bugs, it's
still nicer and makes checkpatch happy.
Signed-off-by: Calvince Otieno <calvncce@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/ZSzapU+eKWvHVwxi@lab-ubuntuSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wlan-ng/prism2fw.c

@@ -725,7 +725,7 @@ static int plugimage(struct imgchunk *fchunk, unsigned int nfchunks,
 
 		if (j == -1) {	/* plug the filename */
 			memset(dest, 0, s3plug[i].len);
-			strncpy(dest, PRISM2_USB_FWFILE, s3plug[i].len - 1);
+			strscpy(dest, PRISM2_USB_FWFILE, s3plug[i].len);
 		} else {	/* plug a PDR */
 			memcpy(dest, &pda->rec[j]->data, s3plug[i].len);
 		}