lmkd: Fix string null termination in proc_get_size and proc_get_name

Fix string null termination and cleanup proc_get_size and proc_get_name
functions.

Bug: 74119935
Test: lmkd_unit_test
Change-Id: Ied176b8d347b672b91866ac59a813d4ff349930a
Signed-off-by: Suren Baghdasaryan <surenb@google.com>