USB: gadget: f_mass_storage: use ?: instead of a macro

This commit removes an "OR" macro defined in Mass Storage
Function in favour of a two argument version of "?:" operator
(which is a GCC extension).

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>