Handle modified timestamps in dmesg lines

The normal kernel message looks like this:
<7>[   55.384215] c0 MXT MSG:02 94 31 2b 83 07 4c 00 13

We have seen some systems that use a different dmesg format, like this:
<7>[11317.428001 / 10-24 04:50:45.331] MXT MSG:1c 91 7b 02 b9 07 41 00 00

Modify the sscanf pattern to accept the second format.

Signed-off-by: Nick Dyer <nick.dyer@itdev.co.uk>