firewire: core: code refactoring to detect both IEEE 1394:1995 IRM and Canon MV5i

The detection of IEEE 1394:1995 and Canon MV5i is just required within
some of the condition branches. In this case, these check can be
capsulated within these branches.

This commit refactors the checks.

Link: https://lore.kernel.org/r/20250908012108.514698-10-o-takashi@sakamocchi.jp


Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>