cli: panic when failed to allocate memory for the history buffer

This commit simply modifies the history initialize function,
replacing the return value by panic with reasons. The calling
chains of hist_init don't have steps explicitly throwing or
dealing with the ENOMEM error, and once the init fails, the
whole system is died. Using panic here to provide error
information instead.

Signed-off-by: Hanyuan Zhao <hanyuan-z@qq.com>