USB: gadget: f_mass_storage: dead code removed

The ep0req_name was never used in f_mass_storage hence it may
be safely removed from the code.  It was a leftover from File
Storage Gadget which used it for debug messages.

Signed-off-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>