spi: cadence_qspi: Ensure check for max frequency in place

spi: cadence_qspi: Ensure check for max frequency in place

Ensure the intended SCLK frequency not exceeding the maximum
frequency. If that happen, SCLK will set to maximum frequency.

Signed-off-by: Chin Liang See <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Stefan Roese <[email protected]>
Cc: Vikas Manocha <[email protected]>
Cc: Jagannadh Teki <[email protected]>
Cc: Pavel Machek <[email protected]>
Acked-by: Pavel Machek <[email protected]>