fix: mount command -t option argument parsing

fix: mount command -t option argument parsing

The mount command parsed device=argv[1] and mountpoint=argv[2]
BEFORE scanning for -t, so 'mount -t fat /dev/hdb /test' set
device='-t' and mountpoint='fat' instead of the correct values.

Rewrote argument parsing to scan for -t first, then collect
remaining positional arguments as device and mountpoint.
Added usage message for missing arguments.