isofs: remove redundant continue statement

The continue statement in the while-loop has no effect,
remove it.

Addresses-Coverity: ("Continue has no effect")
Link: https://lore.kernel.org/r/20210617120837.11994-1-colin.king@canonical.com


Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>