trace: dynamic width format syntax not validated

The dtrace via stap backend cannot support the dynamic '*' width format.

Eric noted in https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg04720.html:

  https://sourceware.org/systemtap/langref.pdf

  section 9.2 printf, states:

  "The printf formatting directives are similar to those of C, except that
  they are fully checked for type by the translator."

  and does NOT list handling for '*' under precision or width.

Some trace events have been merged without checking this:

$ git ls-files|fgrep trace-event|xargs git grep '*\("\|x\)'
hw/block/trace-events:11:pflash_io_read(uint64_t offset, int width, int fmt_width, uint32_t value, uint8_t cmd, uint8_t wcycle) "offset:0x%04"PRIx64" width:%d value:0x%0*x cmd:0x%02x wcycle:%u"
hw/block/trace-events:12:pflash_io_write(uint64_t offset, int width, int fmt_width, uint32_t value, uint8_t wcycle) "offset:0x%04"PRIx64" width:%d value:0x%0*x wcycle:%u"
hw/block/trace-events:13:pflash_data_read(uint64_t offset, int width, uint32_t value) "data offset:0x%04"PRIx64" value:0x%0*x"
hw/block/trace-events:14:pflash_data_write(uint64_t offset, int width, uint32_t value, uint64_t counter) "data offset:0x%04"PRIx64" value:0x%0*x counter:0x%016"PRIx64
hw/mips/trace-events:2:gt64120_read(const char *regname, int width, uint64_t value) "gt64120 read %s value:0x%0*" PRIx64
hw/mips/trace-events:3:gt64120_write(const char *regname, int width, uint64_t value) "gt64120 write %s value:0x%0*" PRIx64