tpm: read burstcount from TPM_STS in one 32-bit transaction

Some chips incorrectly support partial reads from TPM_STS register
at non-zero offsets. Read the entire 32-bits register instead of
making two 8-bit reads to support such devices and reduce the number
of bus transactions when obtaining the burstcount from TPM_STS.

Fixes: 27084efe

 ("tpm: driver for next generation TPM chips")
Signed-off-by: Andrey Pronin <apronin@chromium.org>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>