completion: simplify inner 'case' pattern in __gitcomp()

completion: simplify inner 'case' pattern in __gitcomp()

The second '*' in the '--*=*' pattern of the inner 'case' statement of
the __gitcomp() helper function never matches anything, so let's use
'--*=' instead.

The purpose of that inner case statement is to decide when to append a
trailing space to the listed options and when not.  When an option
requires a stuck argument, i.e. '--option=', then the trailing space
should not be added, so the user can continue typing the required
argument right away.  That '--*=*' pattern is supposed to match these
options, but for this purpose that second '*' is unnecessary, a '--*='
pattern works just as well.  That second '*' would only make a
difference in case of a possible completion word like
'--option=value', but our completion script never passes such a word
to __gitcomp(), because the '--option=' and its 'value' must be
completed separately.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>