dtc: Update the usage helper message

if #define DEFAULT_FDT_VERSION     17
The message
	Blob version to produce, defaults to %d (for dtb and asm output)
should be
	Blob version to produce, defaults to 17 (for dtb and asm output)

This patch fix it, and delete the redundant 't'.

Signed-off-by: Wang Long <long.wanglong@huawei.com>
1 file changed