ACPI / amba: Drop unnecessary check for registered amba_dummy_clk

ACPI / amba: Drop unnecessary check for registered amba_dummy_clk

amba_register_dummy_clk() is called only once from acpi_amba_init()
and acpi_amba_init() itself is called once during the initialisation.
amba_dummy_clk can't be initialised before this in any other code
path and hence the check for already registered amba_dummy_clk is
not necessary. Drop the same.

Signed-off-by: Youwan Wang <youwan@nfschina.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Hanjun Guo <guohanjun@huawei.com>
Link: https://lore.kernel.org/r/20240624023101.369633-1-youwan@nfschina.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>