Staging: gs_fpgaboot: Use octal permissions '0444'

Fixed following checkpatch warning
WARNING: Symbolic permissions 'S_IRUGO' are not preferred. Consider
using octal permissions '0444'.

Signed-off-by: Shyam Saini <mayhs11saini@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>