scripts: kernel-doc: Fix syntax error due to undeclared args variable

The backport of commit 3080ea55 ("stddef: Introduce
DECLARE_FLEX_ARRAY() helper") to 5.10.y (as a prerequisite of another
fix) modified scripts/kernel-doc and introduced a syntax error:

Global symbol "$args" requires explicit package name (did you forget to declare "my $args"?) at ./scripts/kernel-doc line 1236.
Global symbol "$args" requires explicit package name (did you forget to declare "my $args"?) at ./scripts/kernel-doc line 1236.
Execution of ./scripts/kernel-doc aborted due to compilation errors.

Note: The issue could be fixed in the 5.10.y series as well by
backporting e86bdb24 ("scripts: kernel-doc: reduce repeated regex
expressions into variables") but just replacing the undeclared args back
to ([^,)]+) was the most straightforward approach. The issue is specific
to the backport to the 5.10.y series. Thus there is as well no upstream
commit for this change.

Fixes: 443b16ee ("stddef: Introduce DECLARE_FLEX_ARRAY() helper") # 5.10.y
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Link: https://lore.kernel.org/regressions/ZeHKjjPGoyv_b2Tg@eldamar.lan/T/#u
Link: https://bugs.debian.org/1064035


Signed-off-by: Salvatore Bonaccorso <carnil@debian.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>