fx2lafw: fix possible use of uninitialized variable (gcc-4.9 warning fix)

hardware/fx2lafw/protocol.c: In function 'fx2lafw_command_start_acquisition':
hardware/fx2lafw/protocol.c:113:7: warning: 'cmd.flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
   (cmd.flags & CMD_START_FLAGS_CLK_48MHZ) ? "48" : "30");
       ^
scpi_usbtmc_libusb: disable bulk_out clear_halt for Rigol DS1000

fix hangup issue with Rigol firmware version 00.02.02.02.00
scpi_usbtmc_libusb: disable all clear_halt for Rigol DS1000
rigol-ds: fix long memory depth setting on DS1000