crimson/osd/lsan_suppressions: add MallocExtension::Register

```
=================================================================
==80592==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 8 byte(s) in 1 object(s) allocated from:
    #0 0x7f5c76eb6367 in operator new(unsigned long) (/lib64/libasan.so.6+0xb6367)
    ceph#1 0x7f5c76a2fb81 in MallocExtension::Register(MallocExtension*) (/lib64/libtcmalloc.so.4+0x2fb81)

SUMMARY: AddressSanitizer: 8 byte(s) leaked in 1 allocation(s)
```

Signed-off-by: Matan Breizman <[email protected]>

Author: Matan-B

src/crimson/osd/lsan_suppressions.cc

@@ -11,7 +11,8 @@
 
 static char kLSanDefaultSuppressions[] =
   "leak:InitModule\n"
-  "leak:MallocExtension::Initialize\n";
+  "leak:MallocExtension::Initialize\n"
+  "leak:MallocExtension::Register\n";
 
 SANITIZER_HOOK_ATTRIBUTE const char *__lsan_default_suppressions() {
   return kLSanDefaultSuppressions;