msm_rmnet_bam: Do not grab non-RMNET BAM channels

Driver was previously grabbing all BAM channels instead of only
the RmNet channels. Only RmNet Channels will be registered.

Change-Id: Iba48c1a69dcabd6c26b488ec8c89dcd18d9a157f
Signed-off-by: Harout Hedeshian <harouth@codeaurora.org>