libceph: use pg_num_mask instead of pgp_num_mask for pg.seed calc
libceph: use pg_num_mask instead of pgp_num_mask for pg.seed calc

Fix a typo that used the wrong bitmask for the pg.seed calculation.  This
is normally unnoticed because in most cases pg_num == pgp_num.  It is, however,
a bug that is easily corrected.

CC: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org
Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@inktank.com>
Reviewed-by: Alex Elder <7214166e8401b2230f8d77c79af830d7f5f725c8@linary.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs