mon: OSDMonitor: fix the check error of pg creating

mon: OSDMonitor: fix the check error of pg creating

The variable 'pgs_per_osd' set value from 'new_pgs' divided by 'expected_osds',
and its type is integer. So it would remove the decimal point and get smaller value.
This would have problem in some situations, for exmaple:

The limitation of pg creating for one OSD is '32'.
There have 3 OSDs and I want to increase pgs for a pool.
It should be the limitation for creating new pgs up to '96(32 * 3)' at once.
Now, I create '98' pgs for a pool.

In original code, '98' would be divided by 'expected_osds' and get the floating value '32....'
Because of the type which is integer, the 'pgs_per_osd' would be set to 32.
Then the value won't bigger than the limitation and get the wrong result.

Signed-off-by: DesmondS <desmond.s@inwinstack.com>
Fixes: http://tracker.ceph.com/issues/17169