ShellPkg/UefiShellAcpiViewCommandLib: Fix ECC issues

1. Separate variable definition and initialization.
2. Make the variable naming following Edk2 rule.

V2: Remove the updates of guard macros in header files.

Cc: Sami Mujawar <sami.mujawar@arm.com>
Cc: Evan Lloyd <evan.lloyd@arm.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>