scsi: zfcp: fix wrong data and display format of SFP+ temperature

When implementing support for retrieval of local diagnostic data from the
FCP channel, the wrong data format was assumed for the temperature of the
local SFP+ connector. The Fibre Channel Link Services (FC-LS-3)
specification is not clear on the format of the stored integer, and only
after consulting the SNIA specification SFF-8472 did we realize it is
stored as two's complement. Thus, the used data and display format is
wrong, and highly misleading for users when the temperature should drop
below 0°C (however unlikely that may be).

To fix this, change the data format in `struct fsf_qtcb_bottom_port` from
unsigned to signed, and change the printf format string used to generate
`zfcp_sysfs_adapter_diag_sfp_temperature_show()` from `%hu` to `%hd`.

Link: https://lore.kernel.org/r/d6e3be5428da5c9490cfff4df7cae868bc9f1a7e.1582039501.git.bblock@linux.ibm.com
Fixes: a10a61e8 ("scsi: zfcp: support retrieval of SFP Data via Exchange Port Data")
Fixes: 6028f7c4 ("scsi: zfcp: introduce sysfs interface for diagnostics of local SFP transceiver")
Cc: <stable@vger.kernel.org> # 5.5+
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Reviewed-by: Fedor Loshakov <loshakov@linux.ibm.com>
Reviewed-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/s390/scsi/zfcp_fsf.h

@@ -410,7 +410,7 @@ struct fsf_qtcb_bottom_port {
 	u8 cb_util;
 	u8 a_util;
 	u8 res2;
-	u16 temperature;
+	s16 temperature;
 	u16 vcc;
 	u16 tx_bias;
 	u16 tx_power;

drivers/s390/scsi/zfcp_sysfs.c

@@ -800,7 +800,7 @@ static ZFCP_DEV_ATTR(adapter_diag, b2b_credit, 0400,
 	static ZFCP_DEV_ATTR(adapter_diag_sfp, _name, 0400,		       \
 			     zfcp_sysfs_adapter_diag_sfp_##_name##_show, NULL)
 
-ZFCP_DEFINE_DIAG_SFP_ATTR(temperature, temperature, 5, "%hu");
+ZFCP_DEFINE_DIAG_SFP_ATTR(temperature, temperature, 6, "%hd");
 ZFCP_DEFINE_DIAG_SFP_ATTR(vcc, vcc, 5, "%hu");
 ZFCP_DEFINE_DIAG_SFP_ATTR(tx_bias, tx_bias, 5, "%hu");
 ZFCP_DEFINE_DIAG_SFP_ATTR(tx_power, tx_power, 5, "%hu");