ext4: simplify checking quota limits in ext4_statfs()

Coverity reports that conditions checking quota limits in ext4_statfs()
contain dead code. Indeed it is right and current conditions can be
simplified.

Link: https://lore.kernel.org/r/20200130111148.10766-1-jack@suse.cz
Reported-by: Coverity <scan-admin@coverity.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org