sf: Simplify lock ops detection code

sf: Simplify lock ops detection code

Simplify the flash_lock ops detection code and added
meaningful comment.

Cc: Bin Meng <[email protected]>
Cc: York Sun <[email protected]>
Cc: Vignesh R <[email protected]>
Cc: Mugunthan V N <[email protected]>
Cc: Michal Simek <[email protected]>
Cc: Siva Durga Prasad Paladugu <[email protected]>
Signed-off-by: Jagan Teki <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Reviewed-by: Jagan Teki <[email protected]>
Tested-by: Jagan Teki <[email protected]>