usbip: Use _FORTIFY_SOURCE=2 instead of (implicitly) =1

_FORTIFY_SOURCE=2 uses more and stricter checks. This is what e.g.
Debian recommends to build packages with.

While at it fix a typo in the output of ./configure --help.
Signed-off-by: Uwe Kleine-König <ukleinek@debian.org>
Reviewed-By: Hongren Zheng <i@zenithal.me>
Link: https://lore.kernel.org/r/20230503173622.1072787-1-ukleinek@debian.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/usb/usbip/configure.ac

@@ -94,11 +94,11 @@ AC_SUBST([USBIDS_DIR])
 AC_MSG_CHECKING([whether to use fortify])
 AC_ARG_WITH([fortify],
 	    [AS_HELP_STRING([--with-fortify],
-			    [use _FORTIFY_SROUCE option when compiling)])],
+			    [use _FORTIFY_SOURCE=2 option when compiling)])],
 			    dnl [ACTION-IF-GIVEN]
 			    [if test "$withval" = "yes"; then
 				AC_MSG_RESULT([yes])
-				CFLAGS="$CFLAGS -D_FORTIFY_SOURCE -O"
+				CFLAGS="$CFLAGS -D_FORTIFY_SOURCE=2 -O"
 			     else
 			     	AC_MSG_RESULT([no])
 				CFLAGS="$CFLAGS -U_FORTIFY_SOURCE"