uboot-imx

FAT: use toupper/tolower instead of recoding them

toupper/tolower function are already declared, so use them.

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Stefano Babic <sbabic@denx.de>