spi: bcm-qspi: Handle lack of MSPI_REV offset

Older MIPS chips have a QSPI/MSPI controller that does not have the
MSPI_REV offset, reading from that offset will cause a bus error. Match
their compatible string and do not perform a read from that register in
that case.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Link: https://lore.kernel.org/r/20200420190853.45614-4-kdasu.kdev@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>