staging: greybus: firmware: Change long long unsigned to unsigned long long

Fixes checkpatch warning:
  type 'long long unsigned int' should be specified
  in [[un]signed] [short|int|long|long long] order

Signed-off-by: Michael Sartain <mikesart@fastmail.com>
Acked-by: Viresh Kumar <viresh.kumar at linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>