Revert "usbtmc: convert to devm_kzalloc"

commit ab21b63e upstream.

This reverts commit e6c7efdc.

Turns out it was totally wrong.  The memory is supposed to be bound to
the kref, as the original code was doing correctly, not the
device/driver binding as the devm_kzalloc() would cause.

This fixes an oops when read would be called after the device was
unbound from the driver.

Reported-by: Ladislav Michl <ladis@linux-mips.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>