soc: sunxi: sram: Actually claim SRAM regions

sunxi_sram_claim() checks the sram_desc->claimed flag before updating
the register, with the intent that only one device can claim a region.
However, this was ineffective because the flag was never set.

Fixes: 4af34b57 ("drivers: soc: sunxi: Introduce SoC driver to map SRAMs")
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20220815041248.53268-4-samuel@sholland.org