qseecom: correct range check in __qseecom_update_cmd_buf_64

Make change to validate if there exists enough space to write a
unit64 instead of a unit32 value, in __qseecom_update_cmd_buf_64.

Change-Id: Iabf61dea240f16108e1765585aae3a12d2d651c9
Signed-off-by: jitendra thakare <jitendrathakare@codeaurora.org>