mhi: controller: Fix warning in mhi_qcom.c

Initialization function isn't correctly checking the return value of
sysfs_create_group:

drivers/bus/mhi/controllers/mhi_qcom.c: In function 'mhi_register_controller':
drivers/bus/mhi/controllers/mhi_qcom.c:610:2: warning: ignoring return value of 'sysfs_create_group', declared with attribute warn_unused_result [-Wunused-result]

Fixes: bebf2ba4 ("mhi: add snapshot for MHI driver stack")
Change-Id: Ic0dedbad089272344f85e46c18f6218b511f4877
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>