sf: Rename few local functions

sf: Rename few local functions

spi_flash_write_bar-> write_bar
spi_flash_write_bar -> read_bar
spi_flash_cmd_wait_ready -> spi_flash_wait_till_ready

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]>