sf: probe: Fix quad bit set path

Currently, flash quad bit is set in "spi_flash_validate_params" and later
at the end in the same api, we write 0 to status register for few flashes,
thereby overriding the quad bit set. This fix moves the quad bit setting
outside this api in "spi_flash_probe_slave"

Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>