libzfs: Fix missing va_end call on ENOSPC and EDQUOT cases

libzfs: Fix missing va_end call on ENOSPC and EDQUOT cases

The switch statement in function zfs_standard_error_fmt for the
ENOSPC and EDQUOT cases returns immediately and unlike all other
cases in the switch this does not perform the va_end call.

Perform a break which ends up calling va_end rather than returning
immediately.

Found by static analysis with CoverityScan 0.8.5

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4900