This commit increases the hardware SPI frequency from 24.2MHz to 48.3MHz.

[    5.314163] m25p80 spi0.0: speed: 24166666/40000000, rate: 8, prescal: 2, loops: 226
[    5.076323] m25p80 spi0.0: speed: 48333333/50000000, rate: 4, prescal: 1, loops: 162

`time cat /dev/mtd2 >/dev/null` is reduced from 5.64s to 4.36s on A104ns,
and from 11.39s to 8.81s on A1004ns.

Signed-off-by: Sungbo Eo <mans0n@gorani.run>