dyndbg: increase PREFIX_SIZE to 128

A follow-up patch will add the possibility to print the filename as part
of the prefix.
Increase the maximum prefix size to accommodate this.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20230709-dyndbg-filename-v2-2-fd83beef0925@weissschuh.net


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>