Change sb_lock() calls to sbc_lockassert() and remove the sb_unlock() calls in sb_cmd2() and sb_getmixer().  The lock has already be grabbed before these functions are called.
Change sb_lock() calls to sbc_lockassert() and remove the sb_unlock()
calls in sb_cmd2() and sb_getmixer().  The lock has already be grabbed
before these functions are called.

This is a RELENG_5 candidate.

PR:		71189
Submitted by:	stephane
MFC after:	3 days

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