Fix dynamic buffer serve
Fix dynamic buffer serve

It is required to implement FsReadCustom() for
dynamic buffers, otherwise httpd internally
may use already deallocated memory.

Change-Id: I25a308a9f175de7744b2d891d797deb9ee80576d
GitOrigin-RevId: 7cd439358accf1d8dcdbff9a584ad4ec2d39052d

google-coral/coralmicro,google-coral/coralmicro,google-coral/coralmicro,google-coral/coralmicro,google-coral/coralmicro