read-cache: pass repo struct to ce_mode_from_stat()
In other to reduce the usage of the global trust_executable_bit,
add a parameter to the function ce_mode_from_stat(), that will
get passed a repository variable.
This commit uses UNUSED as the next commit will modify the function
to pass the repository parameter.
Signed-off-by: Olamide Caleb Bello belkid98@gmail.com