[SCSI] sd: fix computation of the full size of the device

When computing the full size of the device, we need to cast
sdkp->capacity before shifting, since in some configurations sector_t
can be a 32-bit number.

Also, change ffz(~x) to the more idiomatic ilog2(x).

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/sd.c

@@ -1436,7 +1436,7 @@ got_data:
 
 	{
 		char cap_str_2[10], cap_str_10[10];
-		u64 sz = sdkp->capacity << ffz(~sector_size);
+		u64 sz = (u64)sdkp->capacity << ilog2(sector_size);
 
 		string_get_size(sz, STRING_UNITS_2, cap_str_2,
 				sizeof(cap_str_2));