sound: dapm: Fix compilation error when PROVE_LOCKING is enabled

If the PROVE_LOCKING is enabled then we are getting the compilation
error with SND_SOC_DAPM_CLASS_PCM as undefined. It seems that
the change "3cd04343 - ASoC: dapm: Rename dapm mutex subclass
to better match usage" had renamed this enum to SND_SOC_DAPM_CLASS_RUNTIME
but later the change "dc4479fb - ASoC: dapm: fix race condition in dapm"
didn't follow that name and we didn't get any compilation error
since PROVE_LOCKING feature is not enabled and in the absence of this
feature the 2nd parameter of the mutex_lock_nested "subclass" doesn't
take effect since it becomes macro. Fix this compilation error
by using the right macro name.

Change-Id: I17eb67cb611c00f88986e086bb1b8508d2929af6
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>