builtin-cat: Use getopts to parse command line arguments
builtin-cat: Use getopts to parse command line arguments

Clean up builtin-cat.c by switching to getopts for command line argument
parsing.

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@kernel.org>

penberg/pstore,penberg/pstore,penberg/pstore,penberg/pstore