zgetdump: Fix gcc 7 warning

With gcc 7 the compiler checks for sprintf() the maxium possible resulting
string based on the used datatypes.

Example:

 struct vol {
          ...
          char bus_id[9];
          ...
 }

 sprintf(vol->bus_id, "0.%x.%04x", ssid, vol_parm->devno);

The compiler can prove that "ssid" comes from "u8" and "vol_parm->devno"
from "u16". Therefore the resulting maximum string can be 0.ff.ffff which
requires 10 bytes.

This leads to the following warning:

 dfi_s390mv.c: In function 'volumes_init':
 dfi_s390mv.c:243:45: warning: '__builtin___snprintf_chk' output may be
  truncated before the last format character [-Wformat-truncation=]
  snprintf(vol->bus_id, sizeof(vol->bus_id), "0.%x.%04x", ssid,
                                             ^~~~~~~~~~~
 In file included from /usr/include/stdio.h:936:0,
                  from dfi_s390mv.c:15:
 /usr/include/bits/stdio2.h:64:10: note: '__builtin___snprintf_chk' output
    between 9 and 10 bytes into a destination of size 9
    return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         __bos (__s), __fmt, __va_arg_pack ());
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To get rid of the warning use 10 instead of 9 bytes for the bus_id.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>

zdump/dfi_s390mv.c

@@ -81,7 +81,7 @@ struct vol {
 	u64			part_size;
 	u64			mem_start;
 	u64			mem_end;
-	char			bus_id[9];
+	char			bus_id[10];
 	u32			nr;
 	u16			blk_size;
 	struct df_s390_dumper	dumper;