bam_dmux: Add workaround for modem crash.

Effectively reverts "msm: bam_dmux: Add locking around platform device
calls" (3688ab952920247bc79a1dd89293bd6449fb1127) for at least r530*
family, as this commit is responsible for their modem crash and boot loop.

TODO: Determine exactly why this commit is related to the modem crash, and
why other d2 devices are unaffected.

Change-Id: Iafb7092f448f31c0b5a08c20d9d1921f356014a1

Conflicts:
	arch/arm/configs/cyanogen_d2usc_defconfig