yaffs Changed the logical error handling paths in yaffsfs.c

Restructed the yaffs_open() function to handle errors caused by not using O_CREATE.
Also added  a new yaffs_set_error() function to yaffsfs.c and yaffsfs.h.
An annoying printf in yaffs_fileem2k.c was commented out.
Signed-off-by: Timothy Manning <tfhmanning@gmail.com>