scsi: ufs: Avoid invalid error message in UFS ioctl

This change avoids invalid error message when we query
disk partitions via ioctl by moving NULL buffer check
in function ufshcd_ioctl() inside proper switch case.

Change-Id: Idb3164049d2868953a36f88fce3a982cfd3fe8d6
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>