osd/Watch.cc: pass entity_addr_t by reference

CID 1086832 (#1 of 1): Big parameter passed by value (PASS_BY_VALUE)
 pass_by_value: Passing parameter addr of type entity_addr_t (size 136 bytes)
 by value.

CID 1086833 (#1 of 1): Big parameter passed by value (PASS_BY_VALUE)
 pass_by_value: Passing parameter addr of type entity_addr_t (size 136 bytes)
 by value.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>