checkpatch: always parse orig_commit in fixes tag

Do not require the presence of `$balanced_parens` to get the commit SHA;
this allows a `Fixes: deadbeef` tag to get a correct suggestion rather
than a suggestion containing a reference to HEAD.

Given this patch:

: From: Tamir Duberstein <tamird@gmail.com>
: Subject: Test patch
: Date: Fri, 25 Oct 2024 19:30:51 -0400
:
: This is a test patch.
:
: Fixes: bd17e036b495
: Signed-off-by: Tamir Duberstein <tamird@gmail.com>
: --- /dev/null
: +++ b/new-file
: @@ -0,0 +1 @@
: +Test.


Before:

WARNING: Please use correct Fixes: style 'Fixes: <12 chars of sha1> ("<title line>")' - ie: 'Fixes: c10a7d25e68f ("Test patch")'

After:

WARNING: Please use correct Fixes: style 'Fixes: <12 chars of sha1> ("<title line>")' - ie: 'Fixes: bd17e036b495 ("checkpatch: warn for non-standard fixes tag style")'



The prior behavior incorrectly suggested the patch's own SHA and title
line rather than the referenced commit's. This fixes that.

Ironically this:

Fixes: bd17e036b495 ("checkpatch: warn for non-standard fixes tag style")
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Louis Peens <louis.peens@corigine.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Cc: Philippe Schenker <philippe.schenker@toradex.com>
Cc: Simon Horman <horms@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>