s390/crashdump: fix TOD programmable field size

The size of the TOD programmable field was incorrectly increased from
four to eight bytes with commit 1a2c5840ac ("s390/dump: cleanup CPU
save area handling").
This leads to an elf notes section NT_S390_TODPREG which has a size of
eight instead of four bytes in case of kdump, however even worse is
that the contents is incorrect: it is supposed to contain only the
contents of the TOD programmable field, but in fact contains a mix of
the TOD programmable field (32 bit upper bits) and parts of the CPU
timer register (lower 32 bits).

Fix this by simply changing the size of the todpreg field within the
save area structure. This will implicitly also fix the size of the
corresponding elf notes sections.

This also gets rid of this compile time warning:

in function ‘fortify_memcpy_chk’,
    inlined from ‘save_area_add_regs’ at arch/s390/kernel/crash_dump.c:99:2:
./include/linux/fortify-string.h:413:25: error: call to ‘__read_overflow2_field’
   declared with attribute warning: detected read beyond size of field
   (2nd parameter); maybe use struct_group()? [-Werror=attribute-warning]
  413 |                         __read_overflow2_field(q_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: 1a2c5840ac ("s390/dump: cleanup CPU save area handling")
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/kernel/crash_dump.c

@@ -46,7 +46,7 @@ struct save_area {
 	u64 fprs[16];
 	u32 fpc;
 	u32 prefix;
-	u64 todpreg;
+	u32 todpreg;
 	u64 timer;
 	u64 todcmp;
 	u64 vxrs_low[16];