sound: Fix SEQ_SYSEX() macro

Correct implementation also found in Linux's soundcard.h:
https://github.com/torvalds/linux/blob/master/include/uapi/linux/soundcard.h#L1178

seq_processevent() interprets event[1] as device number and does not
work properly with current SEQ_SYSEX() implementation.

Note: soundcard.h has its own funky style, which this commit follows

Reviewed by: imp, christos
Pull Request: https://github.com/freebsd/freebsd-src/pull/1374