staging:most/hdm-i2c: Replace symbolic permissions with octal permissions

WARNING: Symbolic permissions 'S_IRUGO' are not preferred.
Consider using octal permissions '0444'.
This warning was detected by checkpatch.pl for hdm_i2c.c.

Signed-off-by: Zhengyi Shen <shenzhengyi@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>