libc/stdio: fix wrong characer of open mode flag
libc/stdio: fix wrong characer of open mode flag

This patch fixes wrong character 'X' to 'x' in lib_mode2oflags function.

Change-Id: Ie95e7c5b56c4b6e0647ddb4dfa0021844deef7df
Signed-off-by: Heuisam Kwag <2145cbb01e90577cd4983eccc3b7d9a9dfba6875@samsung.com>

JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT