scsi: ufs: core: Leave space for '\0' in utf8 desc string

utf16s_to_utf8s does not NULL terminate the output string. For us to be
able to add a NULL character when utf16s_to_utf8s returns, we need to make
sure that there is space for such NULL character at the end of the output
buffer. We can achieve this by passing an output buffer size to
utf16s_to_utf8s that is one character less than what we allocated.

Other call sites of utf16s_to_utf8s appear to be using the same technique
where they artificially reduce the buffer size by one to leave space for a
NULL character or line feed character.

Fixes: 4b828fe1 ("scsi: ufs: revamp string descriptor reading")
Reviewed-by: Mars Cheng <marscheng@google.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Yen-lin Lai <yenlinlai@google.com>
Signed-off-by: Daniel Mentz <danielmentz@google.com>
Link: https://lore.kernel.org/r/20231017182026.2141163-1-danielmentz@google.comReviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/ufs/core/ufshcd.c

@@ -3728,7 +3728,7 @@ int ufshcd_read_string_desc(struct ufs_hba *hba, u8 desc_index,
 		 */
 		ret = utf16s_to_utf8s(uc_str->uc,
 				      uc_str->len - QUERY_DESC_HDR_SIZE,
-				      UTF16_BIG_ENDIAN, str, ascii_len);
+				      UTF16_BIG_ENDIAN, str, ascii_len - 1);
 
 		/* replace non-printable or non-ASCII characters with spaces */
 		for (i = 0; i < ret; i++)