f2fstat: fix command-line options

In ARM, the char type is always defined as unsigned (which is allowed
by the C standard).  This caused the terminator return value of getopt (-1)
was being converted to 255 and thus never matched the loop exit condition.

Also printfs warning 'unknown option' has been removed from all the tools
because getopt() itself warns with a message.

Change-Id: I15e6b63162d3db0b07eff6810829fb5d38e5d699

Conflicts:
	fsck/main.c
	mkfs/f2fs_format.c