MLK-20060-2 spi: lpspi: add the error info of transfer speed setting

Add a error info when set a speed which greater than half of per-clk of
spi module.

The minimum SCK period is 2 cycles(CCR[SCKDIV]). So the maximum transfer
speed is half of spi per-clk.

Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
Acked-by: Fugang Duan <Fugang.duan@nxp.com>
(cherry picked from commit d13f9515c1378d778e82a72c24a99892389710c4)