sf: Increase max id length by 1 byte

sf: Increase max id length by 1 byte

So, now SPI_FLASH_ID_MAX_LEN is 6 bytes useful for
few spansion flash families S25FS-S

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>
Signed-off-by: Jagan Teki <jagan@openedev.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagan Teki <jagan@openedev.com>
Tested-by: Jagan Teki <jagan@openedev.com>
Reviewed-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>