arm64: zynqmp: Fix comment to be aligned with board name.

The board was renamed from zc1275 to zcu1275 but name in comment wasn't
updated.

Fixes: 370b0e90 ("arm64: zynqmp: Change zc1275 board name to zcu1275")
Link: https://lore.kernel.org/r/6e4215807f535d2e2b2b8055aa8574c748fe22e4.1704728353.git.michal.simek@amd.com


Signed-off-by: Michal Simek <michal.simek@amd.com>