ARM: dts: broadcom: Fix bcm7445 memory controller compatible

ARM: dts: broadcom: Fix bcm7445 memory controller compatible

The memory controller node compatible string was incompletely specified
and used the fallback compatible. After commit 501be7cecec9
("dt-bindings: memory-controller: Define fallback compatible") however,
we need to fully specify the compatible string.

Fixes: 501be7cecec9 ("dt-bindings: memory-controller: Define fallback compatible")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202507011302.ZqNlBKWX-lkp@intel.com/
Link: https://lore.kernel.org/r/20250701175538.1633435-1-florian.fainelli@broadcom.com
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>