usb: gadget: Fix ep_flush issue on composition switch

Currently if composition switch happens from BAM composition to
NON BAM composition. USB driver tries to flush USB endpoint as
part of composition switch, which is failing. Fix the issue by
performing usb core soft reset before disabling bam for NON BAM
composition.

Change-Id: I60d008341ab2788b2eeae5cc4671bb97ef5b792d
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>