nvme: trace: avoid memcpy overflow warning

A previous patch introduced a struct_group() in nvme_common_command to help
stringop fortification figure out the length of the fields, but one function
is not currently using them:

In file included from drivers/nvme/target/core.c:7:
In file included from include/linux/string.h:254:
include/linux/fortify-string.h:592:4: error: call to '__read_overflow2_field' declared with 'warning' attribute: detected read beyond size of field (2nd parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
                        __read_overflow2_field(q_size_field, size);
                        ^

Change this one to use the correct field name to avoid the warning.

Fixes: 5c629dc9 ("nvme: use struct group for generic command dwords")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>