Don't crash mmd for failing to read zram size

Logging an error instead to make the service more resilient. Since mmd
is a critical service, a crash would trigger reboot and eventually
making the device offline.

Bug: 402781015
Test: manually remove the zram module loading from cuttlefish, and
verify mmd doesn't crash

Change-Id: I7ed45eb9ba4353ff1bb0ce3413a8e3a3ec0b96e6