memory: pl353-smc: Avoid useless acronyms in descriptions

APER does not mean anything, while it seems legitimate to call this
clock the AXI peripheral clock.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20210610082040.2075611-14-miquel.raynal@bootlin.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>