spi: ti_qspi: Fix compiler warning when DEBUG macro is set

clk_div is uninitialized at the beginning of ti_spi_set_speed(), move
debug() print after clk_div calculation to avoid compiler warning and to
have proper value of clk_div printed during debugging.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>