alsaloop: parse_config(): handle short form -B / -E options

alsaloop: parse_config(): handle short form -B / -E options

The usage info documents both short and long form arguments for these:

"-B,--buffer    buffer size in frames\n"
"-E,--period    period size in frames\n"

But the short form was missing from the optstring so it wasn't accepted:

alsaloop -B 123 -E 42
alsaloop: invalid option -- 'B'
alsaloop: invalid option -- 'E'

Fix that.

Closes: https://github.com/alsa-project/alsa-utils/pull/317
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>