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 <bmeng.cn@gmail.com>
Cc: York Sun <york.sun@nxp.com>
Cc: Vignesh R <vigneshr@ti.com>
Cc: Mugunthan V N <mugunthanvnm@ti.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Jagan Teki <jagan@openedev.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagan Teki <jagan@openedev.com>