completions: Collapse declaration and attribute assignment

completions: Collapse declaration and attribute assignment

Previously, the associative arrays for the vendor/subcommands and
vendor/functions listings were split into a declaration of type
(using "typeset") and attribute definition (using "readonly"). On
bash 5.1.16 (at least), this lead to the following error (reported
after enabling -xv to expand and print shell inputs)

  ...
  + . /usr/share/bash-completion/completions/nvme
  # bash tab completion for the nvme command line utility
  # (unfortunately, bash won't let me add descriptions to cmds)
  # Kelly Kaoudis kelly.n.kaoudis at intel.com, Aug. 2015

  # Constant to indicate command has no options
  readonly NO_OPTS=""
  ++ readonly NO_OPTS=
  ++ NO_OPTS=

  # Associative array of plugins and associated subcommands
  # Order here is same as PLUGIN_OBJS in Makefile
  typeset -A _plugin_subcmds
  ++ typeset -A _plugin_subcmds
  readonly _plugin_subcmds=(
          [intel]="id-ctrl internal-log lat-stats \
  ...
  ++ _plugin_subcmds=(['intel']='id-ctrl internal-log lat-stats...
  bash: 'intel': syntax error: operand expected (error token is "'intel'")
  ...

Using the available flags for "typeset" to declare the variables as
readonly arrays resolved the issue (and allows for bash completion
to work as-expected)

Signed-off-by: Brad Mouring <bmouring@gmail.com>