drivers: spi: ti_qspi: do not hard code chip select for memory map configuration

drivers: spi: ti_qspi: do not hard code chip select for memory map configuration

To enable memory map in dra7xx, specific chip select must be
written to control module register. But this hard coded to chip
select 1, fixing it by writing the specific chip select value to
control module register.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>