scsi: ufs: core: bsg: Fix sometimes-uninitialized warnings

Compilation complains that two possible variables are used without
initialization:

drivers/ufs/core/ufs_bsg.c:112:6: warning: variable 'sg_cnt' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
drivers/ufs/core/ufs_bsg.c:112:6: warning: variable 'sg_list' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]

Fix both warnings by adding initialization with sg_cnt = 0, sg_list = NULL.

Fixes: 6ff265fc ("scsi: ufs: core: bsg: Add advanced RPMB support in ufs_bsg")
Signed-off-by: Bean Huo <beanhuo@micron.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Xiaosen He <quic_xiaosenh@quicinc.com>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>