osd/OSD.cc: Use MIN() so that we don't exceed osd_recovery_max_active

Caused by 944f3b73531af791c90f0f061280160003545c63

Fixes: #6291

Backport: dumpling

Signed-off-by: David Zafman <david.zafman@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>
(cherry picked from commit 139a714e13aa3c7f42091270b55dde8a17b3c4b8)

Conflicts:

	src/osd/OSD.cc