ShellPkg/UefiShellBcfgCommandLib: Fix '-opt' option

ShellPkg/UefiShellBcfgCommandLib: Fix '-opt' option

For all other bcfg commands the "#" (option number) argument(s) are
treated as hexedecimal values regardless of whether or not they are
prefixed by "0x".  This change fixes '-opt' to handle its "#"
(option number) argument consistently with the other commands.

Making this change removes a potential footgun whereby a user that
has been using a number without a "0x" prefix with other bcfg
commands finds that, on using that exact same number with '-opt', it
has this time unexpectedly been interpreted as a decimal number and
they have modified (corrupted) an unrelated load option.  For
example, a user may have been specifying "10" to other commands to
have them act on the 16th option (because simply "10", without any
prefix, is how 'bcfg boot dump' displayed the option number for the
16th option). Unfortunately for them, if they also use '-opt' with
"10" it would unexpectedly and inconsistently act on the 10th option.

CC: Jaben Carsey <jaben.carsey@intel.com>
CC: Ray Ni <ray.ni@intel.com>
Signed-off-by: Jonathan Watt <jwatt@jwatt.org>
Reviewed-by: Zhichao Gao <zhichao.gao@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Bi Dandan <dandan.bi@intel.com>