firmware: arm_scmi: Remove duplicate include header inclusion

linux/of.h is included more than once, just remove the duplicate include
header inclusion.

Signed-off-by: Ye Xingchen <ye.xingchen@zte.com.cn>
Link: https://lore.kernel.org/r/202302101520071730986@zte.com.cn
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>