spi: sh_qspi: Replace data types with short ones

Just replace unsigned {char,short,long} with u{8,16,32},
no functional change.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>