fs/hpfs: increase pr_warn level

This patch applies a suggestion by Mikulas Patocka asking to increase
all pr_warn without commented ones to pr_err

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Cc: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>